Funny how you ignore the scenes I mentioned. Nia was insecure of her own worth, but she thought moping around would not help her move forward. She wanted to atone for the sins of her father. She buried her sisters because she wanted to be assured of the value of her kind. She was trying to understand humanity, that was her purpose. Something as compelling as Yoko's, Viral's and Kamina's.

Kamina's development is tied to his father because the essential theme of Gurren-Lagann is the confrontation between the past and the future. The eternal conflicts between those that will come and those that came before.