Honestly in the early part of the manga I hated Kazuya, but ever since the movie arc he has really matured. The moment where he walked in, set up the projector for Grandma and Mizuhara in the hospital and left was really good. This entire date he's actually doing this out of the goodness of his heart. He's a horny kid yeah, but he's not really a bad guy (outside of that one time where he stalked Mizuhara. That was shitty).
I think him being hopelessly in love with Mizuhara is kind of sad tbh, we really don't know how she truly feels about him because of the wall that she puts up emotionally. That part of the story is frustrating because she clearly has to realize that Kazuya loves her.