On his high school graduation day, Mahiru, Itsuki's cousin, informs him that she's pregnant. Only then, a gate of lighting stalks and stalks the two in to the world of Granvania. Inside this property,"Impurities" have now been causing a disturbance to the Stars, eventually plunging Granvania into chaos and disease. And Itsuki, today revealed to be person who is fated to meet with the"Star Maidens", sometimes appears as Granvania's ultimate hope and was thus given the duty to produce"Star Children" and combat the"impurities". And unless the undertaking is complete, Itsuki may never have the ability to come back home.