Although she is a mercenary hired to fight for Fate, she often acts in her own interest, deliberately ignoring orders from him -- and even attacking him out of amusement. She has shown a desire to fight Negi herself. During her encounter with Ala Alba before the final battle, she says she had not joined Fate for the money, but is acting out of a desire for bloodlust and carnage.
is one of the three mercenary children that were hired to help Chigusa.
As Negi's team arrives in the Magical World, a disguised Tsukuyomi was part of a squad lead by Fate to take down the Mahora team and frame them for the destruction of the gate between there and the human world. Recently, she was seen acting as Fate's spy, gathering information on the location and actions of the White Wing. When Fate triggered his battle with Negi in Ostia, Tsukuyomi appeared again before Setsuna, exhibiting a lust for fighting the hanyou. She almost defeated Setsuna and attempted to strip her, even implying that she intended to rape her. However, Setsuna quickly escaped and Tsukuyomi was forced to retreat in compliance with Fate's orders
Tsukuyomi's next appearance is alongside Fate. She showcases her impressive abilities, able to hold her own in a "just for fun" battle against Fate, barely escaping his final attack. She later attacks Ala Alba on their journey to the Gravekeeper's Palace, summoning a swarm of demons to attack them. She briefly fights Negi, only to escape amongst the chaos. She reappears at the Gravekeeper's Palace alongside Dynamis and Fate's partners, and it currently locked in battle with Setsuna. During the Final battle, Tsukuyomi reveals that she somehow came into the posession of the legendary Hina Blade, a weapon so powerful that the demon bound within nearly wiped out the Shinmei Ryu. She surrenders her body and soul to the black spirit of the blade, proclaiming that she will feast on Setsuna's soul. She was eventually defeated by Setsuna after proclaiming that unlike Tsukuyomi, Setsuna has friends to believe on.
During the epilogue, it is stated that she continues to stalk and bother Setsuna and Konoka.
Unlike Setsuna, who uses a single sword style, she uses a sword and dagger style. She also knows how use Onmyōdō Charms.
- Shinmei Ryuu Technique: Tsukuyomi is a powerful swordswoman, a student of the Shinmei Ryuu school and able to match strength with Setsuna during their fist battle, eventually overpowering her during their first encounter in the Magic World arc. The full list of the sword techniques is listed here.
- Ni-no-tachi: Used against Negi to escape his grasp. She hits his elbow with her knee to weaken his grasp, and then combines a kick with the slash of her sword to distance him.
- Zanmaken Ni-no-Tachi: A special technique that cuts a demon without harming the (human) obstacle in front of them. According to Setsuna, it is a technique only passed through the main line. It is also seen used by Kurt Godel, and by consequence, Rakan via imitation.
- Shikigamis: Like Setsuna, Tsukuyomi can summon paper golems to do her bidding. She can also fool her opponent with a shikigami copy of herself, allowing her to sneak attack her opponent during the confusion.
- Code of the Lifemaker: Tsukuyomi has access to a Grand Master Key, allowing her to use the Code of the Lifemaker. So far, she is only seen using it to summon demons to attack.
- Okuoni Yakō (億鬼夜行): Using the code of the Life Maker, Tsukuyomi summons hordes of demons.
- Isshun Sengeki: Nitō Kokutō Samidaregiri (一瞬千激・弐刀黒刀五月雨斬り)
Under the name Tsukuyomi Iwai (祝 月詠), she reappeared in Chapter 37 of the sequel UQ Holder! as a cyborg and one of Ala Alba members. Tsukuyomi stop Ikkuu Ameya from activating the satellite cannon. However, she fails as Kuroumaru Tokisaka appears, throwing several blades at her which immobilize her with lightning. She then approaches Ikkuu one more time, however, he deflects her attack. Tsukuyomi praises him for that and after they introduce themselves to each other, they get ready for battle.
Negima Chou Mahora Taisen 1Tsukuyomi is fought in the fifth battle. She is very dangerous opponent that has high movement and her attack could result in 240+ damages.
While the group was fighting with Aya. Tsukuyomi kidnapped Konoka and Setsuna to Chigusa.
In the another battle she fought alongside with Chigusa.
- In UQ Holder!, a character named Tsukuyomi Iwai appears as a member of Fate Averruncus' Ala Alba group. It has been confirmed by author Ken Akamatsu that they're the same person.