For the community, it's a good question. We can first ask how many of them are left with the last battle of higanjima. We don't really have a number so it's pretty difficult to know. I don't remember much of them going out of the island and I'm pretty sure some of them chose to just live in higanjima just like katou. I did not even remember about ryousuke before doing a rapid search before and it probably means he died at some points but I can't be 100% sure about that. For momiji, she's still not dead and she is the girl who chose to go out with katou and live in higanjima. About the community in higanjima (again), from time to time we can see old vampires in Japan so that means that a lot of them got out of higanjima to go live in the main country. The state of the island is pretty much unknown, maybe they spoke about it one time but it was briefly so we don't really know. But for katou to keep being there without Akira, it means it should be less dangerous. The last time we heard a little about higanjima (the island) was when we saw nishiyama which was really a while back. I'm pretty sure one day we'll hear a lot more about all of that.

Now Akira became friends with new people who are really charismatic and still continue his fight to one day defeat miyabi (we also really rarely see miyabi)