May I ask how she's "manipulative"? She seems to be content with having Hiro do whatever the hell he wants except constantly endangering his own life and his teammates.
In comparison it was Zero Two who was acting constantly like "darling should let everyone else to die and be with me!", so........yeah.
Oh and on the front of people being "selfish", that's just literally everyone in this anime not named Goro, and maybe Futoshi and Kokoro.
No, Kokoro and Futoshi were both pretty selfish in their own ways. Futoshi was/is smothering and self-serving, and Kokoro acts without using her words and can't handle emotional rebuke. That's why she partner-swapped after making that promise to Futoshi. Kokoro at least admits she's a terrible person, though. Futoshi's just naive, despite his pure intentions.
Then again, this is what happens when you pair off emotionally maladjusted children and leave them to their own devices through puberty. I get Werner Franxx's methodology, and it has its merits, but this kind of human social experimentation can only end in tears.