Acony manga

Acony summary:

When Motomi Utsuki moves in his grandfather's apartment, he meets a girl named Acony who claims to be a dead person. Eventually, he gets to know that this place and the people living in the building are not normal. From Baka-Updates: "I am, in fact, one of the dead." So says Acony, a rather mischievous girl, upon her first meeting with protagonist Motomi. Newly moved into an ancient apartment, how will Motomi handle Acony and all the bizarre residents?