Kekkon Yubiwa Monogatari

tales of wedding rings - Satou and his best friend, Hime, have been together for as long as he can remember. So when she tells him she's going back to her home world to get married, his first thought is to follow her and crash her wedding. All goes according to plan, and with a kiss from Hime herself, Satou becomes the new groom! But unbeknownst to Satou, the man who marries Hime is destined to be a hero of immense power and save the world! Is Satou up for the challenge, or is this just too much responsibility for one high schooler to handle?!

(Source: Yen Press)