This was done soon after the SIF 5th Anniversary Special, which Soramaru, Aikyan and Tomoriru hosted (wearing these clothes) after Nico, Yoshiko and Setsuna were chosen as their groups’ representative campaign girls. The other girls joined in with each call and response – which included Aikyan and Tomoriru also doing Nico Nico Nii! as shown here.

Link to the broadcast for reference