Maou no Musuko wa Sunao ni Narenai!

In the distant future, there will be species from different realms that walk this earth and coexist with humans. And of course, not everyone and everything will be peaceful. To combat any conflicts that arise, a new Special Task Force is founded: Soul Justice. The Soul Justice is so strong that they even defeated the Demon King and stopped his quest for world domination. (Don't worry, he has since turned a new leaf as a highly-skilled farmer.) Mamoru Akamichi is Soul Red of the Soul Justice. And although he helped save the world from the Demon King, he remains as upbeat and humble as ever. He protects everybody, even the Demon King's clumsy son, Lulud, who has proclaimed himself to be Soul Red's arch-nemesis. To Akamichi, defeating Lulud is simple as pie, much to the Demon Prince's dismay. Challenge after challenge, duel after duel, Akamichi always comes out the victor. What can Lulud do to conquer his archenemy finally?

(Source: Fantasista Inc.)