Hakoniwa manga

Hakoniwa summary:

Takato's younger sister Utako has always been a frail child - constantly shut up inside the house and not allowed to even venture outside into the sun. But she's cheerful and affectionate, and Takato can't bring himself to be dissatisfied with the situation at home. But when he returns after a semester at his new boarding school in the city, Takato begins to notice changes, not just in Utako but also in his two childhood friends, who seem to know more than they're letting on. And what does all this have to do with an old but infamous urban legend in the village?