A Shinmei Ryuu swordswoman, she is one of the three mercenary children hired to assist Chigusa. Unlike Setsuna who wields a single sword, she employs a sword and dagger style. She also possesses knowledge of onmyōdō charms, similar to Setsuna. Tsukuyomi appears to have a crush on Setsuna, though this is mostly implied rather than explicit, and she enjoys dressing up in Gothic Lolita attire. She and Toko share similar looks (blonde hair, glasses), leading to speculation about a possible relation. After Chigusa's defeat, she returned home.
As Negi's team arrives in the Magical World, a disguised Tsukuyomi joins a squad led by Fate to take down the Mahora team and frame them for the destruction of the gate between the Magical World and the human world. Recently, she has reappeared in another part of the Magical World, finding Setsuna defenseless alongside Asuna.
In UQ Holder, she makes an appearance during the spaceport incident, aiding Fate. It seems that over the intervening 80 years, she has transitioned to nearly full cyborg status and still possesses the Hina Blade. This appearance also provides her with a family name: Iwai.
