Ah, excellent timing. Good work, demons. On the other hand, unless the author is going to eventually reveal that the demons were sent to attack specifically to help this cause by another future-to-past incarnation of the hero or another character, this'll look like a pretty deus ex machina moment.
Still enjoy the level of maturity in some of the writing and world development for a shounen series, just wish the MC would demonstrate equal maturity in being honest in his relationships as he does with his egalitarian worldview. Would make for more satisfying character interactions and development.