This is my honest opinion for the ending,
I hope that they don't end up together.
Not out of spite for how I hate how long this story has been dragged out, or because I hate these characters,
but because I feel this relationship of theirs was built on something very unhealthy.
Kazuya is basically an "niceguys" reddit post, and Mizuhara is toxic beyond belief feeding his addiction to her without giving him a proper reply.
I've had friends in real life who had so many broken relationships because of either of these two types of people
so putting both in the same relationship is honestly a terrible idea to begin with.
The ending of this manga will be "yey we're in a relationship THE END"
but it won't be the end, because that's not how life works. It will continue til their bad personalities eat each other out and push them away.
Just because they get in a relationship isn't a fix for their personality, but maturity will come from it I guess.
I just honestly hope if there's a timeskip after they become a thing, both of them end up with different people and they've matured to be better with the one's they are with then.