She was born on Jurai. She was the granddaughter the emperor who proceeded Azusa. She is also the daughter of Syuuzen Amaki, who would be head of The House Amaki. She manifested a special power allowing her to see everything inside of Tenju by synchronizing with it. When Syuuzen found out, he revealed his true identity as a pirate spy and forced her to spy on certain people. When a prime minister of an ally planet was attacked using such information, Seto managed to figure out the truth through her spy network. However, it was discovered that to manifest her power, she needed the support of The 1st-Generation trees of Jurai and to be cut off from them would mean her death. Through Seto's intervention, Mitsuki is left untouched, but Azusa's uncle agreed to be the fall guy for the incident, as it had become public knowledge that there had been spying. Azusa's uncle was banished from Jurai forever. However, to prevent any more accidents, Mitsuki was placed in a special chamber, which blocked her powers.
Some years later, She saw Azusa walking outside through her window. At the time, he was having difficulty with his training under Seto and Mitsuki felt close to him. She used her powers to cause a transporter malfunction, beaming Azusa into her room. They fell in love and continued to meet in secret. When Syuuzen found out, he revealed it to Kotono, who then sentenced Azusa to death. Seto, however, intervened and blackmailed Syuuzen to drop all charges. Some time later, Azusa is called by The Royal Trees to bond with one of them. However, none of the lower trees or 2nd-Generations would accept him, meaning only a 1st-Generation could. Mitsuki escorts him to the 1st-Generational garden and brings him to her own tree, which she said was now his, and collapsed. She explains she doesn't want to see more people hurt by her, so she cut herself off from the Trees' power and died. Azusa names the tree Kirito and integrates Mitsuki's dead body with it's structure.