Isekai no Maou is a free-to-play RPG available on iPhone, where players assume the role of a powerful demon lord who has been betrayed and resurrected as a spider or slime. The game features over 50 unique monsters to summon, each with distinct abilities, and includes an impressive voice cast from Japan. Players can strategically build their monster army to take revenge against the treacherous heroes.

The gameplay emphasizes strategy and ease of use, allowing players to engage in automatic battles and reap rewards even when offline. Players can evolve their demon lord's powers and fuse monsters to enhance their capabilities. The game also features a competitive arena where demon lords from around the world can challenge each other, aiming to become the strongest among them. The game is rated for ages 12 and includes in-app purchases for virtual currency and items.