Shimana is a teenager ashamed of her own name which can be read as "Turtle Door." Her mother died when she was in middle school; her father re-married some time later. She felt as if she was unneeded in the house, because her new mother didn't pay her enough attention and her father seemed to like her new brother Yuta more, so she decided to escape from home. When she meets Taiga, she is relieved because she thinks Taiga's name is as weird as hers. She started living in Taiga's house together with Zen and Asahi. She fell in love with Asahi at first, but after she discovered that he already have a girl he likes, she couldn't manage to sway his feeling and helped him instead.