After witnessing the death of her family at the hands of bandits, Unchou Kan'u has devoted her life to protecting the innocent by exterminating any group of bandits she comes across. Over time, Kan'u's deeds become famous throughout the land—even if she herself remains unknown. During her travels, she runs across a young girl, Chouhi Yokutoku, whose parents suffered a similar fate as Kan'u's. Finding companionship through their similar pasts, the two girls take a vow of sisterhood and continue to wander the land, determined to bring peace to wherever their journey takes them. During Kan'u and Chouhi's journey, they meet and travel with several people who are sympathetic to their cause, such as the noble Chouun Shiryuu, the headstrong Bachou Mouki, and the calculating Shokatsuryou Koumei. From problems with local lords to groups of ravaging bandits, Kan'u and her friends do what they can to make life a little easier for those in need, wherever they may be. [Written by MAL Rewrite]

The anime Koihime†Musou is loosely based on the eroge game by BaseSon, Koihime†Musou ~Doki ☆ Otome Darake no Sangokushi Engi~.