Is Monster Strike The Animation hentai?
English title: Monster Strike the Animation
No
Rated PG-13 (Teens 13 or older) on MyAnimeList and not tagged as Hentai.

ONA · 2018 · 63 episodes · PG-13 - Teens 13 or older
Action, Fantasy, Video Game
The Angelic Guard, who call the heavens their home, have been tasked with collecting the orbs scattered across the world. Lucifer—a leader of the Angelic Guard with a rebellious streak, said to wield power rivaling the Almighty—carries out her duty along with Uriel, also a leader of the guard. Together, they go about executing their mission, until Holy Magistrate Keter—the one who leads the heavens under the Almighty's will—tells Uriel of Lucifer's planned rebellion. Initially in disbelief, Uriel then learns that the accusations against Lucifer may be connected to an event that once threatened to shatter the heavens. (Source: Official YouTube Channel)
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