Oh yes, she cares about her sister so much, that's why Itsuki slapped the shit out of her, right? Oh Please. That's why she said she would literally burn bridges with her quints to be with Fuutarou before this arc, yes? While Ichika was consistently helping Miku, cinflicted with her own love for Fuuta.
But alas, thanks to the "180" asspulling, the writing wreck, that Negi did in this arc, now 'poor sweet' Nino is the loving one that loved her sisters, and Ichika is the evil villainess that wants to destroy their relationship, until Negi went full status quo at the end of this arc.
All your "arguments" originate only from this arc. Nino has been a bitchy quint even before this, and I dont even hate any quint, I just think she's worst girl
This is why I dont want people replying to me if they disagree, I want to be positive, no fighting, just happy thoughts, happy happy quints because the wars are over