Breaking the Fourth Wall: At the beginning of the episode, Kurumu remarks that this episode will be her Day in the Limelight after the last two episodes were all about Yukari and Mizore.
Distaff Counterpart: The Ghost Brat of Iyo seems to be this for Yukari, his primary ability - to summon pillows to pelt people with - being very similar to her conjuring wash-tubs to bash people on the head with.
Fish People: One of the Captains of Monster Industries is a Sea Monk, a mythological fish man of Danish folklore.
Goldfish Poop Gang: While Monster Industries talk a big game, Tsukune's harem very easily dispatches them without the element of surprise, showing that the humanity was in no real danger from them.
Hot Springs Episode: A portion of the episode is set in a hotel, which has its own hot spring.
Japanese Delinquents: While Monster Industries are all make and dress in male school uniforms, Tsukune's harem (on Rubys recommendation) are all dressed in long-skirted black uniforms meant to evoke the female delinquent, complete with matching make-up and Triangle Shades, Mizore wearing a face mask with a bike chain, Kurumu carrying a wooden daito and Yukari armed with a large set square.
Joke Character: While the other three captains could at least hold up some level of a fight, all the Goblin of Tosa does is snag Moka's skirt with his fishing line. Moka doesn't even need her rosary removed this time, beating him by breaking his mask with a yoyo. He considers his mask being broken as him losing the fight.
Monster of the Week: Monster Industries are an urban gang of Youkai in Shikoku who has aspirations of conquering Japan.
Poor Communication Kills: Monster Industries kidnaps Tsukune as a hostage, they did it because they thought that the Yokai Academy students where there to stop them from conquering Japan (since Yokai Academy's purpose - to live in peace with the humans - is antithetical to their goals), when really they were there on a field trip. When they tell this to Tsukune's harem, they admit they don't care if they conquer the nation or not.
Tengu: Monster Industries' leader the Goblin of Tosa is a long-nosed tengu, his real face identical to the mask he was wearing (though regular flesh-colored).
Unskilled, but Strong: Each of Monster Industries' fighting strategies seems to be pelting their opponent with their attacks with no real strategy or contingencies; the Sea Monk of Awa literally smacking Kurumu with his sheer weight and size, the Wraith of Sanuki conjuring a wall of fire around Mizore and the Ghost Brat of Iyo burying Yukari in pillows. Since the girls have fought various monsters and have equal to higher strength than them, they quickly figure this out and beat them comically fast.
