Kekkon Yubiwa Monogatari

Satou has been childhood friends with his neighbor Himeno ever since she suddenly appeared before him in a flash of light 10 years ago. He resolves to take their relationship to the next level, but just as he's about to confess his feelings for her, she tells him she's moving. He decides that he can't just let her go, so he chases after her. However he gets way more than he bargained for, as his life takes takes an unexpected turn and he is thrust into a world of magic, monsters and wedding rings