The Neglected Pawn that became a Hellspawn

Oscar Storm used to be the shared pawn of both Rias Gremory and Sona Sitiri, but was neglected by everyone in the peerage. They always fond over Issei and Saji, even though their potential is near to nothing.

Rias and Sona always forced the work of both them and their peerages onto him, gave all of his hard work to both Issei and Saji & even punish him for the failures that these have committed.

Tried of being treated like absolute trash, Oscar request Sirzechs and Serafall to be removed from the peerages. After hearing his story and angry at their siblings poor leadership, they agreed.

Now a free devil, they recommend him to Malebolgia, the lord of the 8th Realm of the Underworld.

Once arriving, Malebolgia offers him to become his protege. Oscar wasted no time and accepted his offer.

After sometime has passed, Oscar becomes a powerful warrior in all of the 12 Realms. Alongside his peerage, which he gathered from many of the different Realms, are a force to be reckoned with.

But then, one day; Sirzechs, his Wife, his Son and Serafall came to the 8th Realm. Though happy to see them, the reunion was cut short by a situation: Riser has won the rating game against the combined peerages of Rias and Sona, meaning the two must marry him.

Although he voiced his distaste towards Rias and Sona, he agrees to it because he owes both the Gremory and the Sitiri families a debt.

But how'll things turn out against the former pawn and his ex peerages?