So I see three possible scenarios : 1. Intern-chan is taking Sempai aside to tell him that Douki-chan is after and that he should make a move already 2. Intern-chan is a mastermind that pitted Douki-chan and Rival-chan against each other to keep Sempai all for herself 3. The "Onii-an" is litteral and Intern-chan is actually Sempai' sister
So it was option 1, and Intern-chan confirms her place as best wingman.
