Season 1

High school student Yuge Itsuki was sent off to a strange parallel world with his childhood friend Konatsuki Mahiru. It was the magical world of "Granvania", which was facing a crisis from the threats of "Impurities." Itsuki was summoned to this world as a "Visitor" to save this world, but to accomplish this mission, he had to perform a ritual known as the "Love Rituals..."

Itsuki and Mahiru performed their first Love Ritual. A "Star Child" that will be able to cleanse the Impurity was born, as they bonded through physical contact. Later, they were transferred to "Hoshigami Academy," where the "maidens of the 12 constellations," who will perform the Love Rituals with Itsuki, were gathered. Itsuki starts to bond with one of the maidens, Ruka, at the cherry blossom viewing welcome party.

In order to defeat Impurities that turned out to be far stronger than expected, Itsuki is pressured to perform a "Double Love Ritual" with two maidens at the same time. It is said to produce powerful Star Children, but it has never been performed before. Itsuki steps into uncharted territory, following the lead of onee-san maidens Reone and Falun.

Itsuki bonds with Yuzuha, Maiden of Pisces. She works as a painter, but uses a coffin as bed for some reason, and drew what she saw in dreams while sleeping inside it. She seems to be in a slump, so Itsuki asks her out on a date as a change of pace. Then she shows up carrying the coffin with her...

A beach tour was organized to deepen Itsuki's bond with the maidens. However, that information was leaked to the biggest playboy in the academy, Seiya, who followed them in an attempt to seduce the maidens. While at the beach, Lillith, the fortune teller Maiden of Gemini, predicts that Itsuki will die soon.

Mana recommends Collette, Maiden of Aquarius, to Itsuki for the next "Love Ritual." However, Itsuki becomes hesitant of laying hands on a girl who is so pure and innocent. Despite being plagued by guilt, Itsuki helps out at the bakery where Collette usually works alone, in order to deepen their bond, but...