After Forcing Myself on the Beautiful, Strong, and Tragic Marshal [ABO]

Zi Yusen transmigrates into an O-pretending-to-be-an-A angst novel, in the role of a villainous tool character who abuses the male lead.

The protagonist, Mu Li, is an Omega pretending to be an Alpha. Once the marshal of the Galactic Empire, he is captured when alien invaders bring the empire to ruin. The new emperor strips him of his mental powers, humiliates and tortures him in every way, and forces him to marry a Beta notorious as a human traitor and fond of inflicting abuse.

Everyone thinks Mu Li is finished. Then, five years later, Mu Li makes contact with the human resistance, joins forces with them from within and without to overthrow the tyranny, and tortures the playboy who had humiliated him for five years to death over the course of three days and nights.

...And Zi Yusen transmigrates into the poor guy who dies so horribly.

To save his own skin, he wishes he could put Mu Li on a pedestal. He protects him in every way before the new emperor, and does everything he can to contact the resistance and clear his name, working hard to cast himself as a heroic undercover agent who has endured humiliation and bided his time!

Five years later, the human empire is restored. Zi Yusen weeps with joy. At last, he can retire and live the life he's always dreamed of: Back to Field!

But to his surprise, his "wife" comes to his bed in the middle of the night, tears of delirious relief shining in his eyes.

Zi Yusen: "??? Wait, aren't you an Omega???"

Mu Li: "Try it and see."

Theme: You must change your enemy's thinking to defeat them in action.