Genshin Impact: The Daily Life of Inazuma's Youkai

"Sorry, I cheated," Raiden Ei thought, silently apologizing to Yae Miko and the others in their betting game.

The Thunderous Yougou Divine Machine wasn't just a mini-server; it shared functions with the One System, Ten Thousand Divine Machines—surveillance and data transmission. The One System fed into the Ten Thousand One Intellect on Ritou, but Ei's device linked to her, a demon god, with a signal spanning all of Teyvat—a tech black box beyond comprehension.

Ei didn't always monitor Reisen Riou, but she occasionally checked his moves. He had some talent, and his archery potential rivaled the legendary Sasa Yuri. Recently, she noticed he felt his math skills lacking, needing an upgrade.

Math wasn't big in Teyvat. Only Khaenri'ah and Sumeru dabbled. Though Reisen Riou taught Ritou's islanders via the One System, none grasped advanced algebra—most stuck to basic arithmetic, enough for fishing with parabola and refraction principles. Worldly mysteries didn't concern them; a good life did.

In his past life, Reisen Riou's math was weak—barely enough to avoid washing dishes after a vocational degree. As a youkai phone spirit, math became instinctive. Years of use pushed his theoretical math to LV6 (1.5/100) and applied math to LV5 (39.9/100), barely a mathematician, mastering basic and some high school math. Higher fields like linear algebra or number theory? He knew them superficially, parsing the world through his unique racial ability. His high rating exploited Teyvat's math scarcity; back home, he'd be LV4 at best.

…

Reisen Riou revisited math, digging up past-life knowledge to relearn and understand. It wasn't hard, but his spotty high school math left gaps. Advanced applications existed, but bridging to higher math was a chasm.

He tackled higher math with high school tools. Surprisingly, it worked.

"The Thunderous Yougou Divine Machine boosting my math is amazing," he marveled.

Unbeknownst to him, Ei, with her top-tier demon god intellect, smoothed the path, feeding solutions through the Thunderous Yougou Divine Machine. Her mental labor bridged high school math to advanced applications, subtly embedding knowledge in his mind.

Ei smirked inwardly: Think you can brute-force math? Without me, you'd be stuck at the door.

She stayed discreet, unlike Yae Miko, who played dirty.

"Lord, a calling card from Yurei of Yougou Mountain," Amemuki Uji said, interrupting Reisen Riou's math seclusion.

"What? Let's see it," Reisen Riou said, puzzled.

The card claimed Yurei, hearing from Yae Miko that his "friend" Reisen Riou was the Fifth Scribe, wanted to visit. Bored on Yougou Mountain, with old acquaintances gone and no wish to stay at the Shogunate, Yurei sought to crash with his "close" youkai pal, hoping to "drive around" together.

Reading between the lines, Reisen Riou saw Yae Miko's hand—likely clueless about her motives. Yurei's tactful metaphors avoided offense.

"Let Yurei in—no, I'll greet him myself," Reisen Riou said, heading to the courtyard.

"Trouble you, Brother Reisen," Yurei said, entering.

"No trouble, Brother Black Fox," Reisen Riou replied, using Yurei's alias (a black kitsune). "I hear you're learned. I'm wrestling with math—care to advise?"

"Let's see," Yurei, a refined scholar, said eagerly, but pointed at a symbol. "What's this?"

"A square root," Reisen Riou explained.

"…" Yurei conceded defeat, admitting he couldn't follow. He settled in for two or three months, content as a guest.

Reisen Riou pressed on with math. Progress was slow, but his system's rising proficiency—every point a testament to effort—kept him going.

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