Saikyou Kenja Fuufu no Kozukuri Jijou: Honou to Kouri ga Awasattara Sekai wo Sukue Masu ka?

The Suzaku and Byakko clans have been fighting over territory for generations. Their leaders, Shiranui of the Suzaku and Aura of the Byakko, have dueled countless times, always ending in a draw. "I command you, Shiranui, leader of the Suzaku: marry the leader of the Byakko clan and bear a child! Otherwise, the world will perish." A prophetic shrine maiden appears before Shiranui with shocking news about the future. To save the world, he must marry his sworn enemy?! And their child is destined to be a savior? "Do you know how men and women can have a child...?" But Aura, despite being an unparalleled beauty, is completely clueless about matters of love. During the day they are powerful warriors; at night, these two novices set out on a quest to conceive a child—with the fate of the world at stake! (Source: Kadokawa, translated)