Stuff we know:
1. Hunger is naturally talented with Abduction, the forbidden art of seizing the panoply of others and making them your own
2. Hunger's Soul Evocation, the basic expression of his self, is the Imprisoner
3. Hunger's soul seems to already contain multitudes, given the wording of Inheritor
Considering how quickly Hunger grew in his original world (11 years to the Tyrant's centuries and his raw strength still managed to be greater than) despite the lack of destiny's aid, could there be some factor in our boy that makes him so capable of these feats? There has to be a reason he was selected over everyone else to be summoned, it can't have been entirely random. We can see this in the nature of his Progression to; he frequently has the choices to steal the strengths of his enemies in a way that Seram simply did not.
But what does it mean? Could Hunger actually have the spirits of his dead companions laying dormant at his side? Or would some similar effect be responsible for his potential ability to resurrect his family without drawing the attentions of the Hidden Ones? We need more lore.
The "Evening Sky - Heavenly Tomb" also mentions imprisonment, "a prison spun from time and space" with some more details for us whales only. So add that to the list.
I suspect that the Inner Temple could unlock our soul evocation, Seven Seals/Imprisioner, pretty easily. So that's another magic system we can get, and we've seen how good unlocking magic systems is.