If his chromosomes changed then doesn't that mean his dna changed too? And by that logic doesn't that mean they aren't as closely related as before dna wise?
I was talking about this version:
https://mangadex.org/title/ff09caa3-a990-4dff-a22f-d33d9be38f1c/300-nen-fuuinsareshi-jaryuu-chan-to-tomodachi-ni-narimashita