You accepted an offer from Kiyoko and Yachi to become the third manager of the Karasuno High's volleyball team

You three arrive to the gym

Tanaka and Noya see Kiyoko: happy and excited they run to her KIYOKO-SANNNN!! kiyoko slaps them both

Ukai: claps his hands to get the boys attention Alright boys! That's you new manager! Introduce yourselves!