I dropped this after reading chapter 3. Can I ask if the Incubus finally show up to ask the FMC for help for some vitality and they will do the deed. Then, the author will paint it as "it's just their culture"
I know it was a long long time ago, but in early chapters we had a lot of stuff about how Yutaka had some issues with his childhood friend (Atsuto) and people at his middle school. Go back and look at chap 15-16! It's worth doing anyhow.
On the topic of Chapter 15, I just went back to take a look as per your suggestion, and I just noticed that the last panel of page 3 mirrors the end scene of the volleyball arc, with the trophy and all.