From Throne to Classroom: The Warlord Reborn (English-dubbed)

Betrayed by the Emperor, Leon Thorne, the Prince Regent of the Solarian Empire, reincarnates as a timid high schooler. Shedding his cowardly shell, he crushes the bully Chad Keller and meets Elise Mercer, a classmate identical to his past-life fiancee. After destroying her cursed necklace to dispel its dark magic, he settles the debts of his gambling brother, Jared Thorne. When the Sanctum, including Dexter Cross, targets the Mercer fortune, Leon unleashes his Prime Grandmaster powers. He obliterates their assassins, dismantles the syndicate, and wins the loyalty of Riverton's wealthiest man, Edward Langdon, ultimately redeeming his past regrets.