Shoujo Kenshi Akizuki Ren no Oshikake Harayome Seikatsu: Kozukuri wa Waga Shimei... Jusei Suru made Hanasanu zo!

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Masaaki is an expert in swordplay, but he is disliked by girls because of his pervert behavior. One day, he takes part in a swordplay competition. His opponent is Ren, a cool and beautiful girl, and he somehow beats her. This is the first time for Ren to lose and tells him she will marry Masaaki to give birth to offspring with Masaaki's strong gene. Masaaki's father soon accepts it and Masaaki and Ren start living together...

Source: IGDB