I'm afraid I can't tell you the author of 'the last green valley novel'. It could be a relatively unknown author or a new release that hasn't gained wide - spread recognition yet. You may need to do some research, like checking with literary agents or book clubs that focus on new or niche literature.
I'm not sure specifically as I haven't read it in detail. But generally, it might be about a valley that has some sort of unique significance, perhaps related to nature, the environment, or the people living there.
It's usually a great event with lots of interesting exhibits and activities. There are cosplay competitions, celebrity appearances, and all kinds of comic and pop culture stuff.