Second season of Saikyou no Ousama, Nidome no Jinsei wa Nani wo Suru?.

In a ritual, the Goddess bestows upon 10-year-old children a class that shapes their entire future. As the son of the legendary Sword Princess Fara and Archmage Leon—two of the highest-ranked individuals in their respective classes—Arel seemed destined for greatness. Unfortunately, he is branded as classless and thus unable to naturally inherit any kind of specific skill. However, Arel soon discovers that he can replicate the abilities of any class he desires—though doing so demands significantly more effort than it does for the naturally gifted. Eager to test his unprecedented skills even more by finding stronger opponents, Arel sets out to defy the limits imposed upon him and prove that perseverance can surpass even divinely appointed talent.

The story follows the strongest king in history, Grey. Although he possesses unparalleled power, wealth, and fame, there is no one who stands by his side…and he trusts no one. One day, Grey suddenly meets his death and is reincarnated as a powerless infant named Arthur in a world of magic. Surrounded by a loving family and companions, Arthur starts to experience joys in this new life that he never knew in his previous one. However, during a journey, his family is attacked by bandits... Thus begins his second life, filled with love and adventure! (Source: Official site)

Under the tutelage of the great demon warlock Romberg, Ike grew up with knowledge regarding an ancient advanced civilization that once ruled the land. Coupled with his innate talent in magical arts, this upbringing allows Ike to quickly rise in the Demon Lord's army ranks, leading his brigade to consecutive victories against humans. However, Ike has a secret—he is a human himself. Despite knowing all too well the consequences if this information is ever to leak, Ike is willing to face such immense danger to achieve his goal: find a way for humans and demons to coexist and stop the war that has been carried on for far too long.