Seems like story is going the 'mind/body duality' route. The soul/spirit taking direct control of the body as well as altering reality. Probably how Kuma was able to remain in control of his body even though his brain, CPU whatever was deactivated. To me, it seems like all the different haki powers (CoO, VOAT, etc) are actually one. For top tiers, the only limitation would be imagination and available energy. Is imu even human, and how old are they? If he's been using the same G5-type powers for 1000s of years or more, it will be hard to write a convincing way to beat him by human means alone.
Real question is why does Luffy need to eat food at all lol? He should be able to just manifest it out of nowhere, or is that "dream food" and thus has no energy. DBZ had the best solution to this: strong emotions = energy. Just scream really loud and think of something dramatic. Problem solved hahaha.