Kayou Koukyuu no Hanayome

Overview

Princess Hisui is married to the third prince of a neighboring country, Sakuyao, who is only 10 years old. However, there is a big secret behind this marriage. After learning the truth behind the events, Hisui makes a plan to escape, but Sakuyao finds out everything and stops her in a strange temple. There, someone locks the two of them inside, sets them on fire, and tries to kill them, but Hisui lets Sakuyao escape first and they manage to escape overnight...or so they think. In fact, 10 years have passed outside. Sakuyao, whose age has been transformed, has risen to the position of emperor and announces that he will make Hisui his wife...!? (Source: Akita Shoten)

Source: AniList