Launcher of a Thousand Ships: Shusei has stated that everyone at the Twilight Mansion harbors feelings for Yuki, even him; meaning that Yuki can be paired with Luka, Tooko, Tsukumo, Hotsuma, Shusei, Sodom, Takashiro; anyone actually.
The Scrappy: Many fans resent Yuki for being a Non-Action Guy and requiring to be saved and protected in every single battle, as well as the entire cast adoring him and focusing everything around him. It's implied if not outright stated that this is done on purpose.
The Untwist: If you watch the anime, you will hardly be surprised by the reveal of Reiga’s identity, since you could hear him talk several times in earlier episodes – and when he did, he had Kanata’s voice actor.
Yoko Oh No: Toukou's closeness with her brother causes his fangirls to become very jealous and suspicious of her.