She lost her husband and child during World War II, and nearly died herself when she met a little boy who offered her a strange piece of meat. The child was Masato and the meat mermaid flesh. At first Misa was happy to have a new child in her life, but she grew afraid of the fact that neither were aging, and became terrified of what Masato was capable of. After escaping from him five years ago, she was taken in by an old man whom she later married. About one month ago, the two were in a boating accident and Misa was thought dead until a week later when she appeared with no wounds. Masato tracked her down and forced her to continue to act as his mother figure. She, in turn, tried to take the mermaid flesh from him to prevent him from feeding anyone else it, but to no avail. Unfortunately, Misa failed to become a full-fledged immortal, as the mermaid flesh's effect began to wear off, and her healing powers were getting slower and weaker. Masato then simply told her that he would find a replacement.
She eventually died after being attacked by a Lost Soul which was formerly Masato's nanny, Yukie. Masato shed a tear for her demise before departing.