@HalfCanadian : I pretty much saw what Umi was going to do since moment one, to be honest. He's a slick guy with a ton of money and influence, and the way he's always got that fake smile plastered on his face speaks volumes. He's got a different girl every week, smart, manipulative, powerful, successful and he's used to getting what he wants.
Rent-a-Girlfriend is not really the kind of manga where this guy would be an altruistic wingman for a guy whom he sees as competition for the girl he himself wants. The characters in this series are pretty realistic. In the real world, guys like Umi outmaneuver and destroy their competition. I would say luring Kaz into this party and Umi then telling Mizuhara he wants her with Kaz as the unwitting messenger is pretty much in line with the general craziness that goes on in this series, and also with the sort of guy Umi is here, and as compared to his counterparts in the real world.
The party itself is a fitting setting for Umi to make his move on Mizuhara: "Look at me at home with all these rich powerful people, and here's this pathetic loser, would you really pick him over me?" Kazuya is like a fish out of water in this party. But, Mizuhara loves him because she knows how he really is, from the ferry where he nearly drowned to save her, to the movie he made for her, to his general behavior towards her. Umi didn't do any of that. He sent some retweet, which was just to keep the line open for him to try to get Mizuhara later. He didn't use his clearly enormous influence or connections to get Mizuhara a hand-up in acting, he just watched her struggle and did nothing. Kaz, on the other hand, used every brain cell he had to help her get ahead in life.
Mizuhara may be a tsundere, but she's also a smart, witty, and frankly realistic person. She is a good person. Her and Kaz is a story that's dysfunctional, but he's earned her love and respect, and I think at this point she's being pretty explicit about showing it.
