Michiru is a young, eccentric girl who loves to play with her best friend, Minagi. Whenever she meets Yukito, she enjoys charging into him, knowingly causing an argument.
After Minagi's mother regains her memories, it is discovered that Minagi's mother was planning to name her miscarried child Michiru. It is then revealed that Michiru was a wandering spirit who decided to help a lonely girl on Earth after seeing the trapped Winged Maiden. Michiru explains that she became a physical manifestation of Minagi's unborn sister to help her through her troubles, and now that Minagi is happy and has made other friends, she is no longer needed. Michiru then vanishes.
When Minagi gets home, she receives a letter from her father explaining that his wife has given birth to a baby girl. When Minagi visits him, she discovers the baby is named, and looks exactly like, Michiru.