While testing out the new flight CAD equipment, most of the testers decided to play tag, forgetting that it sucks magic pretty easily. After a few hours, they're already on the floor, too tired from moving.
Miyuki pulling off an Et Tu, Brute? on Tatsuya to persuade him to be the CAD engineer for the competition. Tatsuya even quotes said line.
After Miyuki and Tatsuya witness Erika being immature by being upset with her brother dating Wattanabe-sensei, Miyuki teases her by asking if she has a brothercomplex. Erika gets mad and says she doesn't want to hear that from her.
Just after the competition, Juumonji calls Tatsuya to a private conversation only for him to be a Shipper on Deck for Tatsuya to ship him with either Mayumi or Mayumi's sisters. Tatsuya was bewildered at that.
In order to get back at Tatsuya for calling her small, Mayumi bakes some chocolates for him on Valentines day. Said chocolate has lots of caffeine on it.
While in a room together, Mayumi teasingly asks why Tatsuya isn't thrilled to be in the presence of a beautiful girl, and isn't making a move. He points out the security camera which causes her to ask what if there wasn't one? Tatsuya trolls her by saying that if she was offering herself to him, he would not hesitate to partake in her. She freaks out and goes redder and redder with each word.
In Episode 21: Mizuki and Mihiko are eating lunch together. Even they aren't looking, everyone else is staring at them in either envy or excitement at seeing how it will go.