IDK... his power is "Devil's Fruit" so... I can't tell if Imu ate a Devil Fruit, or Imu's Power allows them to create Devil Fruits and use their powers.
Maybe Devil Fruits are like... actual produce from Hell, and the Ancient Kingdom was artificially producing them, in a way the Mother Sea hated, in the sense they were literally growing forbidden fruit?
It's like Bioshock Infinite, where dragging something from one timeline into another causes distortion.
So, the Mother Sea hates Devil Fruits because they are from another Dimension, and their existence in our Dimension is warping reality in a way the Mother Sea despises?
If the Sea Devil is Imu, is Lili the Mother Sea? Is the Mother Sea Vivi's Shadow, then?
https://www.ancient-origins.net/ancient-places-africa/blue-lotus-0017940
As a dude into gnostic shit, whoever Oda's occult guy is, that dude puts in the work.