Shimaman

Kaminato Hare is a loner middle school student, who doesn't much understand feelings (neither her own, nor those of others). Her parents send her to live alone in a relative's empty house on a rural island. The people Hare meets there are weird, but also kind of nice. First there's her cousin, Akasaki Maayu, who she can't seem to understand at all. Then there are the two close friends, Ukita Sakuya and Nako Kairi, who creep into her house in search of a ghost, and end up deciding that Hare needs to join their team, due to her superior mystery-solving skills. Hare is used to being alone, but it looks like moving out in the country is bringing more people into her life!

(Source: MangaHelpers)