This strip is referring to the 2024 April Fools event in which the idols' self-introduction lines were replaced by Juo Kunio's impersonations.

Update: I was able to find archived links for all of the April Fools voice clips on the Wayback Machine. Enjoy hearing an old man pretend to be six teenage idols (that's how many were implemented at the time):

Hanami Saki
https://web.archive.org/web/20240401042452/https://gakuen.idolmaster-official.jp/assets/data/voice/saki/voice_91.mp3
https://web.archive.org/web/20240401042531/https://gakuen.idolmaster-official.jp/assets/data/voice/saki/voice_92.mp3

Tsukimura Temari
https://web.archive.org/web/20240401042611/https://gakuen.idolmaster-official.jp/assets/data/voice/temari/voice_91.mp3
https://web.archive.org/web/20240401042633/https://gakuen.idolmaster-official.jp/assets/data/voice/temari/voice_92.mp3

Fujita Kotone
https://web.archive.org/web/20240401041945/https://gakuen.idolmaster-official.jp/assets/data/voice/kotone/voice_91.mp3
https://web.archive.org/web/20240401042132/https://gakuen.idolmaster-official.jp/assets/data/voice/kotone/voice_92.mp3

Shiun Sumika
https://web.archive.org/web/20240401042833/https://gakuen.idolmaster-official.jp/assets/data/voice/sumika/voice_91.mp3
https://web.archive.org/web/20240401042908/https://gakuen.idolmaster-official.jp/assets/data/voice/sumika/voice_92.mp3

Shinosawa Hiro
https://web.archive.org/web/20240401042943/https://gakuen.idolmaster-official.jp/assets/data/voice/hiro/voice_91.mp3
https://web.archive.org/web/20240401043038/https://gakuen.idolmaster-official.jp/assets/data/voice/hiro/voice_92.mp3

Himesaki Rinami
https://web.archive.org/web/20240401042720/https://gakuen.idolmaster-official.jp/assets/data/voice/rinami/voice_91.mp3
https://web.archive.org/web/20240401042739/https://gakuen.idolmaster-official.jp/assets/data/voice/rinami/voice_92.mp3