Kitsune no Iinazuke wa Azakeri Warau

When Hagihara Rito was seven years old, he sneaked out of the house in the middle of the night with his cousin, Ichijo Kei, and witnessed a fox wedding. The fox groom fell in love with Kei, and Rito was betrothed to the fox. From that night on, Rito also gained the ability to see supernatural phenomena...!? A story of a broken engagement between a boy betrothed to a fox and a boy who wants to cure his ability to see supernatural phenomena!

(Source: Kadokawa, translated)