Kokuou-tachi no Kekkon

From [MangaPlaza](https://mangaplaza.com/title/0303012317/): The continent of Argaia has suffered from a mysterious plague. By God's divine decree, childhood friends Kamui, the King of the East, and Ryhid, the King of the West, are to be wed to ensure the safety and prosperity of both nations. Although both are initially taken aback by their deity's providence, both men gather their resolve for the sake of their kingdoms' future. It is now their wedding night, and one man must make love to the other. The problem is, who shall fulfill which role?! With king and king in bed, it's a new world for BL. It is a pairing most grand indeed!