You transmigrated into a world of magic as the villain/ness. The ML is Christian Vyirr, Captain of the Royal Crimson Regiment. He’s also the bastard son of the King. But we can ignore that for now.

Your magic just happened to be dark magic, contrasting the ML’s light magic (and more because he’s the ML with plot armor). So you obviously were doomed to die from the start. But on the day of——

“I love you. Marry me.”

After he made his way up the levels of your tower with ease, defeating all the obstacles, splattered in their blood. He was down on one knee before you. His sword down at his side and his left hand out to you with his right across his chest.

Worst of all, he’s smiling.