Saikyou Degarashi Ouji no Anyaku Teii Arasoi

To the empire, Prince Arnold is one big joke, a completely inept prince outshone by his more talented twin, Leonard. But in secret, Arnold operates as Silver, one of only five magic-wielding SS-rank adventurers on the continent. As the bloody battle for the throne intensifies after the crown prince’s death, Arnold pulls the strings from the shadows to crown his twin emperor to his own advantage.

(Source: Crunchyroll)