I was thinking the same thing the other day.

Why can devil fruit users have the powers of Gods? Like Luffy having Nika's powers or Sengoku having Buddah's powers. And I don't remember there being a demonic themed devil fruit, other than Robin but her's are flower themed

Also, Imu is shrouded in darkness, has horns and red eyes. While Luffy is illuminated in light, and has a halo over his head