Chapter 00
“The Station Platform, a Cat, a Train, and Another World”
“…Ugh, this is the worst. Of all days, it had to be today…”
Hayato Kurosu, 38 years old. Born and raised in Osaka.
On his way home from work, as usual, he stood on the JR station platform at night.
Under-eye bags, loosened tie, a heavy briefcase on his shoulder.
Today, like every other day, his spirit had been completely drained after teaching vector proofs to high school seniors.
“Another class tomorrow… ah, I wish someone could take my place…”
He tossed a candy into his mouth and sank onto a bench. That’s when—
“…Huh? What’s that… a cat?”
Across the tracks, a small black figure leapt out.
Fluffy fur, pointed ears. Clearly, it was a kitten.
“No way!? Hey, hey, don’t go onto the tracks!”
The kitten froze in the middle of the rails.
The platform announcement blared: “A train is approaching.” Ahead, a dazzling light approached.
(If I don’t save it now… it’s over!)
His body moved on its own.
He threw down his bag and jumped.
Running. Desperately toward the kitten.
Just before impact, he scooped up the kitten and turned his back—
“…!”
Light and sound exploded. His vision warped, and he felt his body lift into the air.
A ringing filled his ears as darkness enveloped everything around him.
◆◇◆
When he came to, the sky… had changed.
“Huh?”
It was a forest he had never seen before.
Two moons floated in the night sky, and the air was strangely clear. Even the insects made sounds he had never heard.
“Eh, where…? What is this place… am I even alive…? Wait, didn’t I die?”
The kitten was gone. No tracks, no station, no smartphone, no wallet—nothing.
Instead, he wore strangely comfortable clothes, with a small pouch hanging from his waist. Peeking inside… a few herbs.
“…Is this, like, a game world or something…?”
He looked at his hands in shock.
The bony fingers had grown slender and youthful.
His limbs were longer, his abs toned. No mirror, but he could feel it. His body had rejuvenated.
“No way… did I just go back to being 20 or something? What… a bug? Or is this one of those… ‘I got transported to another world’ things…?”
He wanted to believe it was a dream, but the cold night wind felt too real.
Everything pierced his senses as tangible reality.
The next three days were hell.
Communication was barely possible (though surprisingly, Kansai dialect got through), and the combination of sleeping outdoors and hunger nearly broke him.
Desperately walking toward a city, he finally reached a massive stone-walled city—the Gate of Leoria.
When the city guard understood his words, Kai nearly cried.
(Wow… there really are people… civilization is the best…)
◆◇◆
As soon as he entered the city, the enticing aroma of food led him to a street stall.
Skewered meat grilled over charcoal, the scent of herbs teasing his nose.
“Excuse me, one skewer, please…”
“One skewer, three Dars!”
(…Three Dars? Must be the currency. Well, I’ll manage…)
He opened his pouch. Peering inside, his face fell.
“…Huh?”
Not a single copper coin. Completely empty.
So broke that he couldn’t even use a vending machine.
“…Hey, got no money?”
“…Haha… yeah… I don’t have any…”
“…Looks like a traveler. Here, you’re hungry, right? Eat this.”
The stall owner smiled and offered a skewer.
Kai withdrew his hand.
“I’ll just take the thought. Free food won’t taste good anyway.”
◆◇◆
That night, hungry again, he slumped onto the cold cobblestones of a back alley.
He was near his limit. Consciousness was fading.
(…Yeah, I really did die, huh…)
Then, a sound of something collapsing hit his ears.
“…O-old man!? Are you okay!?”
A white-haired elder in a robe lay on the ground.
Blood flowed from his forehead, breathing shallow.
(Whoa… this is bad… I can’t leave him like this!)
Panicking, Kai ran over, chewed some herbs into a paste, and applied it to the wound.
No bandages, so he tore the hem of the robe to stop the bleeding.
After a while, the elder opened his eyes slightly.
“…You… saved me…”
“But I’m not a doctor. I’m a high school teacher… math. Though, that probably doesn’t explain much…”
The elder was silent for a moment, then smiled faintly.
“Your name…?”
“Hayato Kurosu. But… that might be too long here, so Kai will do.”
The elder closed his eyes quietly and murmured:
“Kai… that has a nice ring to it. I shall give you a new name: Kai Cross. It means ‘crossroads.’ A fitting name for one who has crossed worlds.”
“Cross, huh… well… not bad, I guess.”
◆◇◆
Afterwards, Kai was led by the elder to a grand mansion in the city’s depths.
It was the residence of the principal of the Roselia Royal Magic Academy.
The elder was the academy head and a major authority in the magical world.
He listened intently to Kai’s story of coming from another world and said:
“In this world, the concept of mathematics is underdeveloped. Your knowledge… no, your talent, may reshape our theories of magic.”
“…Uh… I’m just a teacher, though…?”
“Coincidentally, the math substitute resigned today. Would you take the role?”
“…Well… I guess I have no choice. I’m hungry, and as long as I have shelter, I could do it, right?”
And so, the former Osaka teacher Hayato Kurosu, transported to another world, began a new life as Kai Cross.
With royalty, villainous noblewomen, and magic.
Candy in hand, Kansai dialect at full blast—
No one yet knew
that this man would become the legendary “bug” to overturn a kingdom.
