Alright, if I were to change anything to make this manga better, it would be the order of events:
1. Kazuya gets dumped by Mami;
2. Kazuya hires Chizuru as a rental girlfriend;
3. They find out about each other's grandmas, university and that they are neighbors;
4. Kazuya's grandmother gets discharged, but Chizuru's doesn't;
5. Chizuru's grandmother has a heart to heart with Kazuya at the hospital, asking him to always be by her side;
6. Kazuya finds out Chizuru is doing the rental girlfriend gig to further her acting career;
7. Chizuru doesn't get the big role she aimed for and her grandmother's condition worsens;
8. Flashback of Chizuru's childhood and her grandfather raising her happen;
9. Kazuya shows up with the idea of crowdfunding and she accepts;
10. Mami and Ruka get introduced as obstacles, Mami one to be overcome and Ruka one to be made ally;
11. Sumi gets introduced to help with the movie and as supporting role for their romance.
As it stands right now, we had a big lot of nothing until finally the plot decided to go somewhere interesting. I was reading this wanting to see how bad karma would hit Mami, but then Ruka showed up and took the role of antagonist to Chizuru, while Sumi, while the cutest bubble of adorableness that she is, didn't do anything until the last date with Kazuya. There is too much wasted time that could have been used to develop a conflict, that got instead used on Kazuya telling the audience how awesome Chizuru is. If we cut all of that, except for one instance of him saying it, we can get a pretty decently paced drama.