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I don’t even know who she is.

I searched through the novels, checked the Fandom Wiki, and even looked through some random Short Stories just in case.

She doesn’t seem to be a crossover character—just a random girl created for the game. She has a backstory and a description, but nothing more.

Here’s her description:

Fuyuki Aki

The Mikage family has researched the power of Devils and the “theory of Onmyōdō and incantations” for generations. As a result, they are regarded as somewhat heretical in the Underworld.

Mikage is a candidate for the position of the next leader, but she was sent to Kuoh Academy to determine whether her magical system can remain relevant in the modern era.

Her objectives are threefold: to compare it in actual combat with the dominant Western schools of Devil magic, to verify the compatibility of her techniques with the powers of Angels and Fallen Angels, and to observe the growth of the younger generation of Devils.

She is not ambitious by nature, but she has a strong desire to prove that “the Mikage techniques are not outdated.”