Mousou Teikoku Chikuonki

Light and Yomi are spending their daily lives happily playing video games. One night when everyone else is asleep, Light receives an invitation from Alpha, a messenger for someone named King. Light and Yomi are then sucked into another world, where they must undertake a quest to rescue Princess Melody from the demon lord. Light thinks this must be his destiny, while Yomi thinks it's kind of annoying. They form a party with Alpha to start their quest. Alpha as it turns out is an AI robot, and he has a program that allows them to raise their levels while slowly continuing their adventure.