After his parents died, Shinpei was taken in by the Kofune family. One day, he returns to his island hometown to attend the funeral of his foster sister, Ushio. Everything should've ended there, and yet Shinpei is told that Ushio's death wasn't an accident, but a murder.
Found this manga by accident and it seems to be similar to Higurashi no Naku Koro ni, supernatural mystery in a rural area. The story reaches "bad endings" and then it loops from the beginning or from some points. From what I've seen the story might focus a bit too much on action in the later chapters though. The beginning almost feels like a proper murder mystery setting.