Yay, a K-On movie poster! Judging from the open blazer and blond hair, I’d say Ritsu is #2 and Mugi is #4. Azusa and Mio wear the same black socks so I can’t tell them apart! Why are you looking at me like that?
UPDATE: Just noticed the black ponytail, so Azusa is #3, which therefore makes Mio #1. I think!