Kosaka needs to just admit she likes Asimo and, win or lose, she'll date him either way. But probably only after he submits his exam, so at least he tried his best up until then. Going tsun about your feelings is generally a bad strategy.
But it sure as hell is entertaining to watch, and one of the more interesting character archetypes to go with for primary love interests, if you have to choose one (any archetype that requires a lot of character growth to get to the point of acknowledging and confessing feelings, really- straight deredere is nice and sugary-sweet sometimes, but spice is life).
The fact that you can have characters that basically hate each other at the start of a story, and, over time with both character and relationship developments, they come to realize they actually love each other by the end... it's probably one of the more engaging ways to tell a love story. And why I personally liked Niseoi by paying close attention to the pair that they were obviously focusing on for pretty much the whole story, instead of taking the low-hanging shy-girl deredere bait that had a glacial-to-static relationship progress rate. The tsun, by comparison, kept having massive development all through the story.
Also, yeah, Nasa with the unintended platonic harem. He's just such a nice guy, and he's super taken, so yeah, he's safe to be around. Almost all the guys in this story are either his family, rivals, long dead historical figures, or only connected to the girls in his life (like Kaname's maybe-one-day boyfriend, Kazumiya, or Kurenai's unnamed boyfriend).