on another note bcs i couldn't put it anywhere in my first comment, but i think MC's younger sister could also be isekai'ed as his little brother bcs all of them were there in that basement at the time of the accident. i don't think kangwu's mention of his little brother was accidental, or how he "grew taller" and whatnot. IDK i myself am skeptical about this particular theory but it is a possibility i think
avoiding uni by reading gay p*rn