wait a min, isnt marrying your sibling illegal- also cant those cause genetic problems and...

I don't know about the whole messed up genetics part because they didn't cover it or I forgot, but the village the mc grew up in encouraged incest because it created offsprings with a lot of power.

Pretty sure this doesn't apply to this manga's rule lol i suppose as thedad said before 5i read it all again lol) marrying your own sibling can make the kid super strong

I forgot about this being in anime and logic and I have forgotten about what the dad said-