Mephisto has no permanent appearance as she constantly changes body to fit her needs and circumstances.
While she was critical of Haunted's personality and how it was compatible with her's, Mephisto is equally as sadistic and sociopathic as he is with being visibly disgusted with the concept of "self-sacrifice". She is also domineering and belligerent from her scene with Reima as she held no sense of partnership with him, rather just using him for her own goals.
Mephistopheles at some point joined Valhalla and an encounter with the Inquisition and had her soul removed from her body and she vowed to take it back from the Inquisition's containment area where it was stored. She was originally ordered by Mother Goose to work in tandem with Haunted but both insisted on working alone.
Festival of Fools Arc Edit
Mephisto assaults a number of the Anti-Magic Academy's Student Council to pry her way into the school without detection. She is visited during one of her attacks by Mother Goose who chastises her on how she was supposed to work with Haunted in both the Einherjar attack and silencing Mari. Mephisto admits that she simply cannot work with someone like him and assured Mother Goose that she will be able to complete her goal on her own.
Mephisto allied herself with the transfer student, Reima Tenmyouji where she gifted him with the Magical Heritage, Tyrving, so they could work together in finding her body while in turn, she would incur a spell to enslave the entire academy to his will. The guise for the campus-wide spell was the reinstatement of the Witch Hunt student festival and Mephisto masqueraded as a student before killing and possessing Shizuka Sendou, the Student Council secretary. Similarly, Student Council President Nagaru Hoshijiro took active interest in Reima's quick rise to become the Ethics Committee Chairman and how her fellow Student Council members were being killed. Nagaru enlisted Ouka Ootori's help but her involvement soon got the latter possessed while the Nagaru herself was incapacitated beforehand.
The possessed Ouka confronted Mari who was working on disabling the school-wide curse and her identity is quickly deduced. Mari is caught in a bad position as she couldn't release enough magic to block the bullet without detonating her Gleipnir. Usagi, who was previously saved from Reima, tackles Ouka off the elevated ground and enter a brief struggle against her before Ouka uses a charm to distract Usagi. Ouka returns to Mari's location at which point, Takeru rejoins the team after dealing with Reima. Takeru is forced out of his Witch Hunter form after being shot by Vlad and buys some time before Usagi returned but Mephisto decides to test their faith in each other. As soon as Usagi reached the roof, Mephisto attempts to fool her into thinking that she transferred her soul to Takeru's body while the latter tries to convince Usagi that she is lying. Eventually, Takeru places his faith in Usagi making the right decision and tells her to shoot him if she feels overly pressured. Mephisto briefly loses her control over Ouka's body when Ouka herself is able to temporarily regain control of her body and yells at Usagi to shoot her. Utilizing the bullets given to her by Ikaruga, Usagi first shoots Ouka where Mephisto's soul is forced out and she shoots another bullet where it dissipates Mephisto's soul for good.
Witch Hunt War Arc Edit
While Mephisto was permanently killed, her body proved to be a vital part of Hayato Kurogane's plan to defect from the Inquisition. He promptly hid the body at an unknown location and shared this information to the Heretic Alliance after his "defeat" by Takeru.
Witch: Mephisto was a powerful witch whose unfortunate encounter with the Inquisition at her soul removed from her body, leaving it an empty but usable vessel. Luckily for her, her attribute specialized in transferal magic that proved to be a substantial threat.
Ancient Attribute- Devil: With her magic-able body robbed from her, Mephisto was still able to utilize her attribute to create numerous amounts of Install Transfer charms to help her forcibly take over the bodies of others.
Host Body Abilities: Unable to inherently use magic anymore, Mephisto's primary means of combat and movement depended on the body she was currently possessing. The potent effects of her attribute paired with the Transfer Charm allowed her access to the host body's abilities where she gained their memories, skills, and even Relic Eaters.
Song of Slavery- Master Slave: The enormous area of effect spell that Mephisto had tried to utilize the students into invoking. Completely subjugates those caught under it.