#Theory
What if Imu's power isn't a conventional Mythical Zoan, but the ability to manifest different forms of the Devil?
The unusual introduction box identifying the power simply as "Devil Fruit" could be a deliberate hint.
Perhaps Imu embodies the primordial Devil, capable of taking multiple demonic forms:
Form 1 – Lucifer: The fallen angel, representing Satan and the false god.
Form 2 – Tzitzimitl: The celestial demon associated with darkness and threatening the Sun, fitting Imu's opposition to Nika.
Form 3 – Apollyon: The abyssal destroyer, with an appearance resembling the eye-covered biblical Ophanim.
Imu isn't one specific mythological demon but the primordial Devil, capable of manifesting different interpretations of demonic beings. It also connects with the "abyss" and how gorosei have different demonic forms (not devil fruits). Imu is literally tapping into demon realm.