落ちこぼれ皇子、気づけば皇帝になってた

A prince is the laughingstock of the entire court. His brothers crush him. The empress despises him. Officials ignore him. Then they frame him for treason and send him to execution. On the scaffold, he smiles. System, activate. Suddenly, the army rebels. Generals march on the capital. The prime minister tears up the death warrant. Treason? He calls it a promotion.