LogFAQs > #936451049

Because the games are the same other than the appearance, and whether the dialogue refers to the character as her father or brother. There's not actually any real difference other than the context of the story, and the context of the story is way better with him as a father.

If you say start getting into the actual background grimmoire lore and side content OUTSIDE of the game, there's big differences, but in game...basically nothing.

So it just boils down to in game brother Nier being a generic loser nobody jRPG protagonist that would fit into any throwaway game, and Papa Nier actually being unique.

There is one line with Emil that is notably different between the two, that has more to do with a facet of Emil than Nier.