DxD: Fusion

Koneko Perspective

Koneko Toujou sat cross-legged on the battered, overstuffed couch of the Occult Research Clubroom, cocooned by the warm, toasty scent of sakura mochi and the faint, old-wood aroma that always seemed to hover in the air. She held a glossy sweet bun in her lap as if it were a tiny animal she might befriend, and nibbled a mochi between her teeth, the soft pink rice staining her lips for a moment before she licked it off.

On the low table in front of her, a neat grid of sweets—melon pan, matcha jelly, a single refrigerated custard—waited as tribute. If the others noticed her silent system of organization, no one had ever said.

Her golden eyes flicked lazily toward the door as the faint hum of teleportation shimmered through the room.

A flash of red light, bright and elegant as a stage curtain. Rias Gremory stepped through first, the club president's crimson hair briefly tousled, her posture impeccable as ever. She moved like someone who had rehearsed every entrance and never missed her mark.

Trailing close behind, Akeno Himejima floated in with a flick of violet-black hair and a wry smile. She had that supermodel glow, that effortless grace, but her eyes always seemed to be in on a joke Koneko wasn't sure she wanted to hear.

Rias brushed at her skirt and nodded toward Koneko. "Good afternoon, Koneko," she said, her voice a practised blend of warmth and command, like an older sister who was also, somehow, a CEO.

Akeno flopped elegantly into a club armchair, one arm draping over the back, and gave a little wiggle of her fingers. "Stockpiling snacks for the apocalypse?" she teased.

Koneko munched deliberately before answering. "Maybe."

She didn't say it out loud, but the snacks helped. They always did. Even before she'd joined Rias' peerage, sweets were her sanctuary. And after Rias had saved her, taken her in without judgment, Koneko had begun to understand what it felt like to belong. Even now, she didn't fully know what she wanted in life—but at least she wasn't running anymore.

Rias sat beside her, smoothing out her skirt. "Sirzechs and Toshio will be here soon."

Toshio.

Koneko blinked. Her thoughts shifted instinctively. The first time she'd seen him, she thought he was weird—quiet but not shy, too calm, always watching things with those unreadable eyes. And then he'd started walking with Rias.

He'd started showing up in the clubroom after class occasionally, always with a she had never heard of. He'd never ask to join the conversation, unless he was here with a specific purpose, but he'd never turn away if someone pulled him in. He'd spar with Kiba sometimes, and sometimes he'd win—though Koneko suspected he was holding back more often than not. He never gloated. Never grinned. Just accepted the result, win or lose, and moved on.

But what Koneko remembered most was how he treated her. He never forced his presence on her. Never filled the air with questions or tried to coax her into talking. He just sat nearby, sometimes reading, sometimes just breathing, and let her be as silent or as loud as she wanted.

She started sharing sweets with him on accident once—left a taiyaki on the table and came back to find half of it gone and Toshio reading in the corner. He'd looked up and said, "Good pick."

After that, it became a thing. She would often share her snacks with him. He would always be appreciative. Koneko had begun to think he was calming to be around, well, once she was sure he wasn't just some 'hentai'.

Now, as she listened to Rias and Akeno talk about the upcoming visit—the "Very Important Guests," as Akeno called them with a little sing-song voice—she found herself glancing up at the clock, measuring the seconds until Toshio would show up. He was always on time, never early, never late. She wondered if he'd stop by the vending machines first, or if he'd wander in with his hands in his pockets, hair slightly mussed from the breeze. She wondered if he'd notice the extra sweets she'd set out, or if it would be one of those days when he left something behind for her instead.

She told herself she didn't care either way. It was just snacks. It was just a habit.

Due to her heightened senses, her ears pricked up at the faintest sound—a shoe scuffing in the hallway, the rattle of a doorknob, the creak of the old wood flooring. She could feel his weird energy, just a tiny bit, that always distinguished him as unique. It wasn't magical or demonic power, nor was is ki or, senjutsu. It was just, Toshio.

Then the door creaked open.

He entered, uniform crisp, posture disciplined, but never stiff. His movements seemed calculated yet effortless, as if every mundane gesture was a precise movement with no wasted energy that he never even paid attention to. Toshio Amano, the swordsman, the oddball, the enigma nobody ever managed to decode—not Rias, not Akeno, not even Koneko herself. Though she felt like she had gotten just a little closer the more time she spent with him. It was nice to be around someone like her.

"Speak of the swordsman," Akeno purred, her voice a velvet drawl as she carried in a tray of tea with a sway to her hips.

Rias perked up. "How did it go with Sona?"

Toshio shrugged, a slight, one-shouldered gesture, and dropped his bag with a muted thump by the door. "Exactly like you said it would," he replied. "She tried to recruit me, I told her no. I even almost beat her in chess. She didn't like that."

Rias laughed, light and genuine, her hand fluttering to her collar as if to keep from grinning too hard. "Did you tell her why you turned her down?"

"More or less. I think she got the hint."

He moved to sit beside Koneko on the couch, the cushion dipping under his weight. His proximity brought a brush of cool air scented faintly of a forest in autumn.

Koneko glanced at him, then at her bun, then at him again. Without conscious thought, she broke off a corner and handed it to him, her fingers not quite touching his. It was a small, silly ritual, but it felt less like a habit and more like a contract. He accepted the piece without a word, only a nod, and the gratitude in his eyes was so subtle it almost disappeared.

But not to Koneko. She saw it, and she filed it away.

He surprised her by gently patting the top of her head, ruffling her hair just enough to be noticed, but not enough to be offensive. It was so unexpected her body locked up in place. Heat spiked from her cheeks to her ears. She looked down and lowered her head, not resisting in the slightest.

"H-Hentai," she muttered.

Toshio blinked. "What?"

"Y-You touched me," she mumbled. She would never admit it, maybe even to herself, that she really enjoyed the contact.

"I was thanking you," he said.

"With your hand. On my head," she clarified, with the icy clarity of a judge passing a sentence.

Rias suppressed a laugh behind a manicured hand. Akeno grinned, sharp-toothed and conspiratorial.

"You're really not used to affection, huh?" Toshio's tone softened, the edge of teasing swapped for something quieter, almost understanding.

Koneko scowled—at herself, mostly—and looked away, her gaze fixing on a crack in the clubroom wall. "Not from you," she said, which was both a lie and the truest thing she'd said all afternoon.

He tilted his head. "Should I stop?"

She thought about it for half a breath. "…Maybe not," she whispered, barely audible.

"What was that?" he asked, leaning closer.

"Nothing," she snapped, then risked a sidelong glance. He was still looking at her, calm and unbothered. That made her feel somehow safer than she liked to admit.

The moment collapsed when Rias cleared her throat, posture straightening to full-on president mode. "Toshio, I have some good news for you," she announced, eyes shining.

She smiled, bright and proud. "I was able to sell a few of your nuclear reactor designs and schematics."

Toshio froze. For a second, Koneko saw him unguarded—genuinely surprised, maybe even touched. Then he leapt to his feet and, before anyone could react, wrapped both arms around Rias in a spontaneous hug.

"Are you serious?" he blurted.

"Dead serious." Rias grinned, red hair spilling over his arms.

"Rias, you're amazing." Koneko thought it was a little weird seeing him this excited for once. Just how much money had those things been worth?

In that instant, the room ignited with stubborn, swirling crimson, and a new weight pressed down on Koneko's senses—greater than anything she'd ever known. Sirzechs Lucifer materialized in a spiral of runic symbols, his presence swirling around the clubroom like a sudden drop in atmospheric pressure. His suit was immaculate, his smile as guileless as a child's, but his eyes—sharp, cunning, and ancient—missed nothing.

Toshio let Rias go and stepped back, but just a little too late.

Sirzechs' smile was far too innocent.

"Am I interrupting something?" Sirzechs inquired, with the air of one who very much planned to interrupt everything.

Rias scowled, her cheeks a pink echo. "Onii-sama."

Sirzechs turned a gaze on Toshio that could have evaporated steel. "So this is the mortal who's been touching my sister?"

Toshio raised a hand, deadpan. "Strictly above the neckline."

Akeno laughed, struggling to contain it behind her dainty hand, which left even Kiba grinning from his seat behind his book.

Once the laughter faded, Toshio's demeanor shifted. "Satan Lucifier, it is an honor to meet you." Toshio bowed in respect. The Satan smirked slightly.

"The pleasure is mine, I assure you, Toshio Amano, was it? And please, call me Sirzechs. I hear that title enough in the underworld." His tone was a cross from neutral and slightly friendly, though it likely betrayed how he was feeling.

"Yes, sir. And just call me Toshio."

He straightened, and the faintest edge of determination crept into his voice.

"Sirzechs, about Ghom."

The air thickened. Even Akeno's mirth at the situation faded.

Sirzechs's jawline tensed. "It won't take long. I plan to eliminate it myself right now before I take Rias her peerage back home," he announced, as if reading from a proclamation.

Toshio shook his head, resolute. "Don't." Koneko had to respect Toshio just a little for basically giving an order to a Satan.

Rias turned, startled. "What?"

Toshio met Sirzechs's gaze, and Koneko saw there was no fear in him—only a stubbornness that bordered on recklessness. "Ghom is my responsibility. I want to be the one to end it," he said.

"Can you seal him off for now, keep him from hurting anyone?" Toshio inquired. Sirzechs had a glimmer of curiosity in his eyes.

"I may be able to. Why?"

"I need the chance to reach that level. To prove that I can."

Rias opened her mouth, probably to protest, but Toshio held up a hand. "I won't do it alone," he said, softer. "Not again. You, or someone else, can be on standby if I can't handle it. Just give me until the end of break."

A silent standoff crackled between Toshio and Sirzechs. It was impressive that Toshio could stand up to the imposing presence of the devil king. Finally, the Lucifer exhaled, and the room's oppressive weight lessened a hair. "That's a dangerous delay," he warned.

Toshio's eyes didn't waver. "So is never knowing what I'm capable of. Plus, I have a score to settle," he countered, the words heavy as iron.

After a long beat, Sirzechs sighed. "Fine. I'll seal off the area he's in. But he's on borrowed time."

Crimson magic shimmered and he vanished.

Koneko glanced at Rias, expecting her to be angry. Instead, she looked… emotional. Not quite sad, not quite proud. Something in between.

"You okay?" Toshio said.

"Toshio, why would you try to go after that thing again, you know what he did to you last time. I couldn't bear to see you like that again." Koneko had heard a brief description of Toshio after Rias saved his life. It must have been really bad if Rias was this scared of letting Toshio try again.

Toshio pulled Rias into a gentle embrace. "Things will be different this time. I'll be ready. I'll be okay, I promise." He looked into Rias' eyes with determination, a look that Koneko couldn't help but feel a little warm inside from. Rias rested her head on his shoulder. Koneko couldn't help but stare, a tiny longing in her chest that she couldn't describe forming.

"You better be okay. Because if you're not, I'll reincarnate you and make you regret breaking that promise." It sounded like a joke, but she said it in a worried tone that dissipated the humor.

"I'm glad your brother was so understanding. At least with Ghom. He doesn't seem to appreciate it when we do this."

Rias pulled back and rolled her eyes. "He's such a dramatic older brother."

"Thanks for speaking up for me," Toshio said.

"Careful," Akeno purred. "If you keep hugging Rias like that, Onii-sama might catch you. Maybe you should redirect your efforts to me. I don't have any angry siblings."

Rias narrowed her eyes. "Akeno..."

"Kidding," Akeno sang, "mostly."

Toshio snorted in amusement. "I'll keep that in mind."

He turned back to Rias. "By the end of break, I'll be strong enough to kill it."

She smiled, warm and fierce. "I'll hold you to it."

She glanced at the clock. "We should go. Onii-sama will be back soon."

Stepping away from Rias, Toshio went to Kiba first. They bumped fists.

"Don't slack while I'm gone."

"You either."

Then Toshio knelt beside Koneko, his presence sudden and close. He rested his hand on her head, just for a moment—a simple, steadying pressure.

"I'll make you something sweet when you're back."

Koneko's cheeks heated again; her hands fidgeted with the hem of her skirt. "Okay," she replied. It was just a word, not even a promise, but it felt like opening a window in a stuffy room.

He moved on to Akeno.

She wasted no time and hugged him immediately, one leg wrapping around his waist. She leaned in for a kiss, Toshio's eyes widening slightly in surprise.

A glowing red magic barrier popped up between their lips.

Rias. Arms crossed. Eyebrow raised.

Toshio snorted. Waited. When the barrier dropped, he kissed Akeno on the cheek.

"Eager aren't you?"

Akeno pouted, half-thrilled, half-frustrated.

Rias yanked her away, then pulled Toshio into a long hug.

He held her back.

"I'll miss you, Rias."

"Break will be over before you know it," she reassured him, though it didn't sound like she quite believed it.

Toshio leaned in and kissed Rias' cheek.

Right at the moment, like the gods of comedic timing interfering, Sirzechs teleported in.

He took one look at the scene and flared with palpable irritation. "YOU—"

Toshio shot out of the clubroom in a blur of Shunpo.

"I'LL MISS THE REST OF YOU TOO!" he shouted as he vanished. He even grabbed his bag that was by the door.

Koneko stared after him.

She touched her cheek. Her fingers were a little warm.

Rias exhaled and leveled a glare at her brother. "We'll talk about that later, Onii-sama."

Sirzechs didn't even look at her. "He kissed you."

"Later," she ground out.

He narrowed his eyes, but accepted his sister's terms.

Koneko frowned.

Maybe next time... she'd get a hug too.

Soon after, they all left in a red flash to the Gremory estate.

XXX

Toshio's Perspective

The sun was already slipping toward the horizon, bleeding soft orange through the treetops as I made my way toward the forest clearing I'd long since claimed as my training ground. It was quiet out here—the kind of silence you only find when you're far from people and expectations. Just trees, wind, and the weight of your own thoughts.

Perfect.

My thoughts wandered, inevitably, back to the ORC earlier that day. Rias, flushed but beaming after I hugged her over the fusion circle deal.

Damn, have time to see how that was going to work.

Then Koneko, stiffening like I'd zapped her when I patted her head. Akeno trying to wrap a leg around my waist and trying to kiss me. And Sirzechs... appearing in the exact worst moment, glaring like he was ready to vaporize me with a glance. The guy was scary in that princely way. Graceful. Terrifying. The embodiment of barely-contained power. And yet...

He'd listened. More than that—he'd agreed. Ghom would be sealed, not slain. That was a victory.

I rolled my shoulders, loosening the stiffness still clinging to my limbs. I'd needed a win. Any win.

As I walked deeper into the forest, my reiryoku pulsed gently under my skin, always alive now. I was grateful it could stand in for mana. Apparently, to the system and to the magic circle scripts, there wasn't much difference—just energy, given shape and intent. But the more I studied the formulations in the grimoire, the more I realized they were simplified. Almost... educational. Like training wheels. The real circles? They were deeper. Layered. Fractal.

That intrigued me.

My routine had grown more rigorous lately. Physical training came first, then cultivation with my sword. My sword spirit remained silent during it, but her presence never left. I could feel her, just beneath the surface of the water in my Inner World. Watching.

Something rustled nearby.

My eyes narrowed.

There it was again.

A flick of a tail.

A sleek black cat sat under a tree, green eyes gleaming in the low light. The same one I'd seen a few times before—once after the dojo, occasionally walking through Kuoh, and again the day after I fought Ghom. It wasn't subtle. I had a pretty good idea of who it was.

I crouched. "You again."

The cat didn't flee.

I reached out, palm down.

It padded forward. Headbutted my hand.

I scratched gently behind its ears. "Definitely not a normal stray."

After a moment, I picked her up. She let me.

Cradled in one arm, she was warm and content. Purring.

"Observe," I muttered

{Name: Kuroka (Disguised)

Level: ??

Condition: Relaxed, Amused

Threat Level: A

Descriptive Insight: A high-level nekomata disguised in feline form. While her current threat level appears lower due to her transformation, she remains a master of senjutsu and youjutsu—capable of rapid escalation if provoked. Current demeanor indicates minimal hostility, but ongoing vigilance is advised.}

Like I expected.

Kuroka.

Not that I was even a little surprised to see her here—she'd apparently been tailing me (sometimes literally, sometimes figuratively) for a while now. Likely due to me being close to her sister.

In fanfics, she'd always been a wild card. Seductive, dangerous, but brilliant in her own way. A master of senjutsu and youjutsu, both disciplines I barely understood. There were some small details about poison, stealth, traps—all sorts of things that I remembered here and there.

She played the lazy seductress, but it was always calculated mischief. Master of senjutsu, youjutsu, and, if rumors were to be believed, more than a bit of poison and hand-to-hand. But what really drew my interest wasn't the misdirection or the poison. It was her ki control. Pure, undiluted life energy, used in the form of senjutsu, Toki enhancing her body. There was a reason even the devils gave her the wide berth and why she was the most wanted supernatural fugitive alive.

Ki was rare. Versatile. I didn't care for the fluff surrounding nekomata lore or illusions, but raw ki? That was worth pursuing.

And this one was hiding in my neighborhood, disguised as a stray.

I reached into my bag, pulled out a small wrapped chocolate square.

"Want a treat?"

She sniffed it. Then snapped it up with zero hesitation. A soft purr rumbled through her.

"That was homemade," I muttered. "Just saying." Chocolate would normally make a cat sick, if they even ate it. Considering who it was though, I wasn't worried.

She rubbed her cheek against my collarbone.

I carried her to the edge of the forest clearing I had been training at, then set her down near a mossy rock. "Feel free to watch."

One flick of the tail. Approval, maybe.

I stepped into the clearing and began forming circles.

Ten spells. I could summon all of them now without calculation delays. The system absorbed the incantation component entirely, freeing me to focus on the formulae—on the math.

Create Flame. Create Frost. Create Sparks. Create Water. Create Ice. Create Earth. Create Wind. Create Light. Create Minor Illusion. Mana Circulation.

Most of them sat at Rank 5.

Except Create Flame.

It had become something of an obsession these past eleven days. And after running it several times now, I could feel it—the shape of the circle, the way reiryoku flowed more efficiently into the formation. The incantation-free benefit the system gave meant I could drill the spell on pure structure alone. It felt clean. Close.

I sat cross-legged at the center of the clearing, hands poised in open focus, letting the mana pattern form again and again. Each glyph burned brighter. Smoother. Tighter.

Then, after thirty minutes of constant repetition, I felt the shift.

{Create Flame Rank Up! Rank 10}

Right on cue, a new system notification chimed.

{New Spell Skill Unlocked! Flare

Spell Type: Offensive - Projectile Description: Basic fire attack spell. Travels quickly and dissipates on impact. Useful for igniting things.}

I raised a brow. "Just igniting things huh?"

Another window opened.

{Secret Quest Unlocked: Master of the Basics: Get all basic elemental Create spell skills to Rank 10 within 14 days.}

Of course. The system had opinions about my work ethic.

Challenge accepted.

I summoned the new spell. The magic circle hung in the air like a fractal snowflake, every line and spiral perfectly tuned for fire. I pointed at a dead branch overhead.

"Flare."

A jet of fire shot forward. Not very fast. It was like the speed of throwing a tennis ball. Not terrible for my first real spell. 

Behind me, Kuroka inhaled sharply. I glanced back. She was still perched on her rock, but her eyes were wide, unblinking. There was a hunger to her attention now, a focus that said she was seeing more than just a neat trick. Was what I did really all that impressive?

"Still here?" I called over my shoulder.

She didn't answer, so I walked over, knelt, and gave her a gentle scratch behind the ears. She leaned into it, eyes half-shut.

"Didn't know that would impress you," I said.

The purr that followed was louder, almost pleased.

I returned to the center and got to work dissecting the Flare circle. This was the real meat of it for me: breaking down the spell's structure, seeing which lines did what, theorizing improvements and risks. Human magic, as far as I could tell, was almost entirely math. No symbolism, no prayers, no invocations of ancient names. Just pure, raw calculation, rune symbol and placement memorization, and physics.

I wanted to see how far I could take that.

"Alright," I murmured. "Let's increase the launch speed by twenty percent."

I adjusted the inner arc, tweaked the ratios. Adjusted a velocity matrix. Reduced the stabilizing buffer. Reiryoku gathered. Each change felt like tuning a piece of machinery—one wrong move and the whole thing would seize up, but get it right and you could run it all day.

I tried again.

"Flare."

The spell backfired, detonating about six centimeters from my palm and filling my face with smoke and the brittle smell of carbon. I staggered back, coughing, blinking tears from my eyes.

The cat was still watching.

Kuroka's body was shuddering. She was trying not to laugh.

Cats don't laugh. She wasn't very good at this whole disguise thing huh.

"Yeah, yeah," I muttered, fanning the smoke. "Don't rub it in."

For the next hour, I tried to change the formula for different effects, but it failed every single time. Eventually, I gave up trying to change the magic circle, and just stuck to the original. I wondered what would happen if I got this spell to rank 10.