he isn't Japanese, his paste life is peasant that why he's so surprised to be able to choose his clothe (cuz it's quite luxury that a peasant can't afford)
not sure if he reborn in a same world from his paste life or not
if this dude can turn invisible then why did he let himself get caught by MC? he thought MC was there to "catch" him so he wasn't planning on teaching him originally...
Seeing the mc as genius hyped the mysterious guy, thus, teaching the mc some advance fundamentals kinda makes sense but giving such item really doesn't make any sense..
Also every character here feels somewhat lacking in a sense idk
It doesn't actually matter... it's an RPG Fantasy among many RPG Fantasies... even if you did understand it, you'd probably forget it....
Authors used to have freedom to make powers more complex back when people read less stuff, so complexity would make things stick... but as people got access to more and more stories, too many details and complexities actually make things harder...
Okayyyy, forget about being mathematical scientist, he's doesn't even seem to be from "our blue planet"🙃😂 (because of that not so relatable and interest kinda half-dead)
This "lost person" seems more like reincarnated person(from bluey) than mc😅