The skull of summer

It was the warm day in summer, Yamada got the skull with the letter from his ex-wife. That letter says, "Please bring this skull to somewhere with you, as if the skull is me." Yamada is scared about that skull and letter because he feels that is his ex-wife's curse. In the same time, he looks back about her. Their marriage was not very happy though. Yamada is immersed in his past with his ex-wife, but he ignore that letter, and throw the skull away because he still hates his ex-wife. However, when he gets back home, the skull comes back in his room.