I sympathize with the MC. Regardless of how she looks or how nice she is, Serena brings more work and responsibility when she appears. For a guy who chose a mercenary's life, the MC is absolutely allergic to responsibility.
Miku doesn't know game. If she ordered a different drink, she could snag an indirect kiss with Sou under the pretense of trying each other's drinks. I'm sure Karina and Hinata will do so.