Even Though I'm Invincible, I Can Only Obediently Be Her Guardian

I'm a genius. (Because I held out for ages against three goblins in my first battle.)

I'm invincible. (Because I diligently practice by swinging my sword five hundred times every day.)

I killed the Demon King. (Because I wanted to master some awesome magic.)

My wife is the Demon King's daughter. (Because her mother entrusted her to me.)

My wife wants to become an adventurer. (Because she caught me cheating with her mother.)

In the end, I became my wife's guardian.

"My new book, Stop Your Berserk Behavior, is being updated alongside this one."