This story provides examples of:
- All Girls Want Bad Boys: Rokugou's attraction to Cygnus.
- Anti-Villain: Cygnus, who holds many types but is primarily a Noble Demon.
- Batman Gambit: Frequently employed by Cygnus to further his plans, Konoka uses one against him at the end of Scheme!? so he would waste his then barely-out-of-control powers.
- Bound and Gagged: Poor Rokugou... Cygnus has an attack that induces this, Konoka's turn might be coming soon...
- Boss Fight: Used and lampshaded in Nightmare!?
- Came Back Wrong: Akira Ookouchi, Type 4, forced by Cygnus to prevent her from becoming a Type 2 naturally.
- Chess Master: Konoka, Chao Lingshen for the good guys. Cygnus is the villain for this trope.
- Drunk on the Dark Side
- Crouching Moron, Hidden Badass: Himeko.
- Eldritch Abomination: Cygnus Cantus.
- Enemy Within / Split Personality: Anti-Asuna, who isn't really evil but is something more akin to Asuna's nobody, and Asuna's Heartless, which is the Enemy Within part.
- I Am Legion: Lirael, since all the mermaids are failed clones of herself.
- Let's Get Dangerous: Most of the PPD cast
- Reluctant Monster: Sonic, during most of Nightmare!?
- Shout-Out: Just about everywhere. The entirety of Nightmare!? is a shout out to the Castlevania franchise, certain fights play out like boss fights from certain video games, etc.
- Stealth Pun: Dialogue in Episode 9:
"What the hell is up with Lirael?!" - Becky
"Same thing you get when you cross an elephant with a rhino." - Asuna
- Stockholm Syndrome: Rokugou and Cygnus. The other characters don't like this, fearing Stockholm Shnozzing. ironically enough, Cyg's biggest rival Konoka does not care.
- Tomato Surprise: The chupacabra in Act I turns to be Sonic the Hedgehog, or rather Misora Kasuga masquerading as Sonic the Hedgehog, stalling for time on Chao's orders until the real Sonic can show up.
- Wake Up, Go to School, Save the World: How the story begins, but averted and takes a backseat to the issues at hand.
- With Great Power Comes Great Insanity: Cygnus's One-Winged Angel form, Rokugou's armor card, an inversion with Himeko's armor card, which makes her less spacy and slightly more aggressive.