Summary:

I am the Demon King Sarthis. If I go according to the script, I, the Demon King should be defeated by the Hero on the destined night every five hundred years. After that, I can gloriously leave the field and live as a couch potato.

I’ve been working diligently for this purpose for hundreds of years, and finally, I met my fated opponent. As a result, this guy is so weak he couldn’t even pierce through the first layer of my armor with his ultimate move.

……What methods could I use to lose to this Hero? Urgent, waiting online!

Translator has this to add:

Cute short comedic novel about a demon king who really, really, wants to retire.

If this novel sounds familiar, you might have read it before on another site. I’m the original translator, just moving most stuff over here, plus getting back into translations.