Miss Akyuu, why do people call it Obon?

Obon, or Bon festival, is officially referred to as the Ghost Festival. People shortened it to Obon because it's refers to the tray they used as the container to put the offerings for the ancestors.

Miss Akyuu, what are these two doing?

They are Bon & Shougatsu, two comedians who only appear in the Idol Swim Meet.

The two comedian working as cheerleaders in the Idol Swim Meet.