Koichi and the members of the Mad Hatters band, Akira, Hiroto and Daiki attend a mixer with some sophomore girls from Naruhata Women's College. The girls introduce themselves as Rin, Hina, Kaori and Kazuha. They start chatting and having some drinks with Koichi acting awkwardly all the while. Kaori leaves to fix her makeup and asks Kazuha to come along with her. In the restroom, Kazuha takes off her wig and is revealed to be Kazuho and Kaori turns out to be Midnight in disguise.
It turns out that the Mad Hatters invited Koichi to a Mixer, since the leader had refused to participate because he did not want to feel like he was betraying the girl he loved. Koichi accepted the invitation, much to Kazuho's disgust. Later, Midnight had run into Kazuho as the latter was tailing Koichi on his way to the mixer and recognized her as Pop☆Step who she had met at the first Narufest.
Midnight is on a mission to root out groups who are distributing Trigger at mixers, with the culprits usually being those who organized them. Midnight sees the main suspect of the incidents, Rin Yaritezawa, accompanied by her friend Hina, and outlines plan to also participate in the Mixer together with Kazuho. Midnight telephones the Midnight Boys to distract the other two girls who would join the Mixer, getting them to cancel their participation, and so she and Kazuho take their places as "substitutes".
In a flashback, it is shown that this mission was originally intended by Naomasa Tsukauchi to be a task handled by Shota Aizawa but the latter refused, saying he did not take on assignments that required high-energy and instead recommended Midnight to tackle the task.
Back to the present, Midnight tells Kazuho that the band members are free of suspicion as they knew them from Narufest, leaving only Rin and Hina as their suspects. She tasks Kazuho (as Kazuha) with keeping Hina's attention while she herself would monitor Rin and they return to the mixer to begin with their mission. Kazuha strikes up a conversation with Hina and finds out that she is one of Rin's friends and is always with her.
Meanwhile, Rin starts becoming resentful of the entire situation, being forced to organize the mixer with a band she didn't think highly of, accompanied by an awkward Koichi on top of having to be with two girls she had never met in her life, with Kaori having taken charge of the festivities.
She gets up to leave but collapses and throws up on the floor, Koichi rushes to her aid and she is touched by his concern. Hina snatches away the towel they used to clean the mess and runs to the bathroom to lick on it, becoming insanely jealous at the others fussing over Rin, especially Koichi, and prepares to use some Trigger.