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"!?