>>280755079Keep the original design with the exposed navel.
Make the flame spirit an edgy male spirit that wants to burn the world and has to be kept in check through willpower.
Make The flame spirit work like a burning armor that delivers powerful attacks but slowly consumes Otr's body and the area surrounding it so Otr can't overuse his powers and needs to rely on other abilities.
Make the first big villain an ice shota that has the upper hand until Otr's spirit goes nuclear (badly injuring Otr in the process) and humbles him without killing him, prompting him to be bullied by his fellow ice guys until he abandons them.
Make Six appear after the big confrontation, make him the bearer of another spirit and let him train Otr to control his flame spirit.