Seiken to Bikini Armor

Fiona, a female knight who hates anything vulgar, decides to defeat the succubus king to restore her kingdom, which has become rife with lewd jokes. However, the legendary sword becomes connected to her comrade Lupi's "sensitive parts," causing him pain every time she slashes! To win, she needs to make him feel better...but that's something she absolutely doesn't want to do. (Source: Kadokawa, translated)