I would be really happy if the series ended this way:
Chizuru makes her rightful choice and doesn't tell her grandmother (who turns out to have known anyway), Kazuya finally realizes that the film is an excellent way to say goodbye and breaks off their friendship. Miraculously, he has realized she does not know how to love him and his idiocy meant that he couldn't have truly loved her.
Years later, five maybe, they meet again. They're both married or engaged to someone else. Chizuru is a stylish, somewhat hardened actress, maybe married to that other actor. Kazuya hasn't gone through any miracle cure, but he is considerably more self-confident and better looking.
Fantasy would be that Kazuya would be together with Sumi. Kazuya actually had discovered that he wanted to be a producer and their film gave him a starting point to make a pitch to a film school.
Kazuya and Chizuru have a meaningful, short conversation of about ten minutes. They walk away, pretending that it didn't bother them.
Independently, they agree that the best decision either one of them made in their friendship was that she almost stopped taking his money.
The End