Kodaka stands up to three guys to protect Sena in Episode 3 of Season 1 by putting his delinquent face to work.
When Aoi comes to shut down the club, Sena has her father make Maria an official teacher (basically) and then she tells Aoi to Shut Up, Hannibal!.
Sena: Silence, Mongrel. Let me make one thing clear. Even if the student council had filed to disband our club, I could just destroy it. Be grateful that I chose to get us a moderator instead of justshatteringyour reputation. Aoi: I-I wont accept that! Sena: Listen, Mongrel. This club is mine. If you keep barking in my garden any longer, I will CRUSH you like a bug. Do you want me to get you expelled?
Rika using the balls to make Kodaka realize that he should stop running away from the open affection all the girls are giving him.
The OVA contains one of note, courtesy of Sena. As revenge for monsters gang-raping her during Yozora's portion of the relay novel, Sena humiliates Yozora during her part, only to get smacked around and ordered to lick her feet. But rather than comply, Sena steals the flyswatter, hits Yozora, and says, "Like hell I'd ever lick your feet!" before calling her an idiot and running out of the room. It was immensely satisfying to see for those who were made uncomfortable by Yozora's part.