The hugely popular monster-raising MMORPG: 【Monster・Evolve・Online】, commonly known as 【MEO】. Seventeen-year-old high school girl Kokoro begins a laid-back life in the world of MEO with the weakest monster, a slime named Lime, as her partner. But even though she was just playing with her slime and diligently working on potion-making, before she knew it she had become a 『Slime Master』!?