From WinningDays

Touma Outa wakes up from a bad dream one morning and when he sees his reflection, there are horns growing out of his head. Suddenly, he is pounded in the head by a cute, hammer-carrying knight from the demon world. The horns shrink, but he is not off the hook yet, for the little knight, Pukateriosu, is there to prevent him from transforming completely into the Demon King whose soul has entered Outa's body. The PukaPuka hammer can return him to normal but it takes time to charge. In the meanwhile, Outa must try not to think worldly thoughts or be kissed, but it's easier said than done with his crush Shirayuki Himeka, the little demon Garbelion, and even Pukateriosu around...