Katsura Yuki is a very frail girl, most of her life she had lived inside her room in the hospital with only her nurse and doctor as the only family she considered.

She soon died due to her illness and after a month of her death she was reincarnated into the body of a baby boy, Yukimura Sei.

Now Yuki is living her/his life as Sei but past doesn't disappear even after your death.