I wouldnt worry. Iruma has Dekira's backing. And if their hearts are so similar in terms of musix to poro, I actually woulsnt be surprised if iruma is half demon, half human, what with his survival instincts when he was small. But regardless of him being completely human or not, I also wouldnt be surprised if demonic magic starts to make him become a demon because theres gotta be something different about the demon world and a human staying extended periods, not to mention the heartbreak possibly incoming because lets face it,
iruma as a human will die faster than a demon's lifespan, and asmo and clara will literally do everything possible to not have him die first, esp if what we seen of the misfits class consider iruma to be. Lets not mention sullivan and the others who consider him a grandson, or any of the other demons he inevitably charm by just being so similar to dekira.