Kisaragi Saya is a lonely, introverted high school girl whose inconspicuousness is so subtle that it could almost be called a curse. During her summer vacation in her first year of high school, Saya killed time by playing the MMORPG "Shadow Assassin's World." Even in the world of Shadow Assassin, where monsters and monsters roam, she demonstrates her inherent inconspicuousness and begins to make her presence known as "Kuro," a top-class "ninja" player. Then, Hikari, an extroverted ninja, appears before Kuro, asking to become his apprentice...!?