Kekkon Yubiwa Monogatari

Ten years ago, Princess Hime escaped her world and arrived in Japan, where she formed a close bond with Haruto Satou. When the time comes for her to return home, fulfill her royal duty, and marry another prince, Haruto refuses to lose her and follows her through the dimensional gate.

He arrives just as an Abyss monster attacks the wedding, prompting Hime to marry Haruto instead of her intended groom. Her ring grants him the power of light and reveals his new role: he is the Ring King, the warrior destined to defeat the Abyss King. To gain the full strength required, Haruto must form bonds with four more princesses who possess elemental rings. Chasing his childhood love thus becomes a journey across kingdoms where marriage, trust, and affection are literally tied to the power needed to save the world.