@Menhir : you have to read between the lines here. Aside from what Umi pulled last chapter, (saying "I want you" to Mizuhara through Kazuya,) in this chapter, he took a happy Mizuhara aside to talk to her, and immediately after they were done talking, she was upset but thoughtful and left Umi and his party, making sure to grab Kaz and take him with her. Umi's words very clearly took somebody who wanted to be there, and made her NOT want to be there.
Once alone with Kazuya, instead of tsundere mode, she talks to Kazuya about relationships, knowing full well that he loves her. Also, go back earlier in this arc, where she comes back to Kazuya with food and says to him in a full-cell: "let's eat." That is a facial expression a girl reserves for her boyfriend.
So, seems pretty clear to me.
@WhisCalifa69 : Thank you for your vote of confidence, but Kaz and Mizuhara still have Mami to worry about, and that woman is like a nuclear war of hatred and spite. I don't think they're at "happily ever after" yet. Mami's voice actress in the anime described her as "the last boss," which is pretty accurate.