Deep under the ground in the capital city of Tokyo exists the forgotten and confined world called Tokyo Underground. Rumina Asagi encounters Ruri, an escapee from the Underground, as well as her assistant Chelsea, and decides to protect them. But rather than attempting to bring Ruri back, the Underground's secret organization, "Company", sends over an intelligence personnel by the name of "Supei". Having fallen in love with Ruri, will Rumina take on "Supei" in a battle to protect his love?