Want to help me brainstorm for a story?

I want to make a Manga. I want it to be type fantasy story with alot of wierd characters. I don't know wether to make in in earth of in a different world. Each character has his own problem and flaw that they must solve using different tactics along the way of solving their main problem, which I cannot decide which one it will be, I have a few in list but I don't think they're strong enough. I want all my main characters and one villain to go through a significant character ark, and I want the story to be able to have some funny moment, sad moments, trajic moments... I would like it if the story would start out where they at first alot of things go wrong, but later on it gets better and better. I really don't know how to start out the story, though I have other parts where I like alot and I want to keep. I already know which characters will dies in the story along with all the character's personalities and some of the characters' problems. Any Ideas? What would you add?