If a summoning spell is performed, a summoner could call and bind a monster to fulfill their desire in exchange. Youta, a solitary young man, decides to test the simple spell to have someone to talk to. Despite being told that he's not talented in summoning, he sets his expectations low.
However, Youta astonishes himself by summoning Mumu, a dragon locked in darkness for 300 years! Initially, Mumu intimidates him, but as they converse, Youta realizes that Mumu wants to chat, just like him! They soon develop a friendship, but Mumu is an excessively emotional and dependent dragon. Now coping with her daily bizarre antics, Youta seeks a way to handle his new quirky dragon companion.
