Madoi's sister finally returns to his life after a lengthy absence and she quickly reveals why she'd left: To devise a method to permanently kill Shiro.
Combat in May contains the following examples:
- Chekhov's Gun: This chapter isn't the first time Mayoi's inventions will come in handy.
- Deconstructed Trope: Shiro's Tempting Fate and getting hit by a car are Played for Laughs, until the narrative describes the scene and sounds of the aftermath when she lands back on the ground.
- Elegant Gothic Lolita: Masaki is kidnapped and forced to dress as one to be given away as the prize for the boxing match's winner. It's also revealed the outfit comes from Mashiro's personal collection.
- Fanservice: Mizuho, Ao, and Sanae as Round Girls during the boxing match.
- Lethal Joke Weapon: It turns out that the rubber band gun Mayoi created really was capable of incapacitating Shiro!
- Noodle Incident: Mayoi learns it's very easy to blackmail Shirou simply by mentioning a past one between him and Kasumi.
- Tempting Fate: Shiro claiming that she isn't afraid of getting hit by a car as it wouldn't hurt her... right before she gets hit by a car.
- Rape as Comedy: Both Mayoi and Ao are secretly given stimulants that put them in hormonal overdrive on separate occasions during May. Their target: Masaki of course.
