Since time immemorial, Japan has been protected by five magical crystal pillars that hold back monstrous shades, sustained by barriers maintained by five powerful clans of magic practitioners. Hana Ichise was born into a branch family of one of these clans but has been dismissed and cast aside as weak by her parents, who favor her talented older twin sister, Hazuki. On her fifteenth birthday, a great power suddenly awakens in Hana, but she decides to conceal her newfound abilities in order to someday live a quiet and free life.

Three years later, Saku Ichinomiya, the new and powerful head of the main Ichinomiya clan, is seeking a bride strong enough to stand by his side and help maintain the barrier around one of the pillars. He discovers Hana's true talent and sets his sights on her, in contrast to her sister who was considered a candidate by others but lacked the necessary strength. Hana reluctantly accepts a contract marriage with Saku, motivated by a condition that promises her one billion yen and a house in the countryside if she fulfills the terms of the agreement.

The story follows Hana as she navigates her new position, which forces her to finally use the powers she has worked so hard to hide. While she initially dreams of a peaceful retirement away from the world of magic practitioners, she becomes increasingly embroiled in the conflicts between the magicians. As she develops sincere feelings for Saku, who becomes determined to win her heart, her plans for a quiet future begin to crumble.

The series is set in a modern-day Japan with a secret supernatural society governed by wealthy, powerful families. Beyond the initial marriage contract setup, notable narrative arcs include Hana being tested by Saku's family and facing harassment at school, as well as the emergence of a shadowy organization called The Skull of Nirvana that steals dangerous talismans. This event introduces rival clans, such as the Nijouin family, including twins Kikyou and Kiriya. Kikyou, who harbors a crush on Saku, becomes a persistent challenger seeking to prove Hana unworthy of being the head's wife.