Author just randomly threw in that girl is his half-sister why?

I think it makes sense...in a way I can't explain

The fact that they still use the omega village to surrogate their children is probably why.

It probably does, the author just didn't explain (〜￣△￣)〜

From what I understand, it means that no matter how many heads change, From the older generation in his past life to the new generation with the young head, nothing changed for lunas because their ugly ways won't. Jaheon stopped believing in helping them achieve a better future for lunas because all they want is to use mugo as a scapegoat for all their horrendous acts and benefit from it without making anything better