DanteMustDie
A few questions: × Did Harry inheriting Sun Wukongs' power give him any form of immortality? × Does Harry have the 72 Transformations? It seems a lot like an overpowered Metamorphmagus ability to me. My speculation is that Harry did not inherit this ability but it instead awakened and overpowered his latent Metamorphmagus ability from his Black ancestry (assuming Dorea Black as Grandmother).
Please don't let all the training Rias is doing with Harry be useless. What I dislike about most DxD fanfiction is how stagnant Rias and other girls are. It would be best by the time of the Rating Game with Riser, Rias can destroy him without any need of Harry's intervention. As for evil pieces, a high class devil is necessary to regulate demonic power. Any being that's not born devil will not have any idea or instinct for controlling demonic power. That's the reason stray devils often mutate because of uncontrolled demonic power. Even if that's not the case, I don't think it's a viable option to just let all the reincarnated Devils be without any monitoring.