Hagure Yuusha no Aesthetica, Shinmai Maou no Testament Recommendations
-Both MC are heroes
-Both daughters of the demon king become MC's little sisters
-both involve battles and ecchi stuff
Both of these animes involve a badass male protagonist who protect the daughter of a previous head villain(now deceased). Both animes have good ecchi scenes and neither protagonist hesitate to kill or do what is best to protect the ones they care for.
Suddenly, the main character, who happens to be a powerful hero, adopts the daughter of the Demon Lord and, why not, a whole harem. Somebody should tell them that you're not supposed to fantasize about your sister.
both have the main character who is a hero and at the same time a traitor
the female protagonist is the daughter of the demon king who is now in the care of the protagonist