Living for centuries may seem appealing at first but trust me, the boredom will get to you eventually. That's the main reason that we demons even deign to spare our time to heed summons from mortals. At least, that's how things used to be. There hasn't been a single summoning from Earth in close to 50 years. After that long period of silence, I was called to Earth by a pathetic and broken man. He begged me to live the rest of his life for him. Begrudgingly, I accepted. Apparently the human world has been beset by dungeons - nightmarish portals full of monsters that wreak havoc if left unchecked. Their coming also created those who had supernatural powers and were blessed to be able to grow as if they were video game characters. These individuals are called adventurers. It's natural for a demon to lust after power and the thrill of combat, exactly the lifestyle that being an adventurer provides. The only problem is that my new body is pathetically weak, not suited to becoming even a F rank adventurer. Well, that doesn't matter. I'll climb to the top of the food chain and step over anybody who gets in my way. Don't blame me though, it's just my nature.