Amusingly, Ryo has turned up in three other comics -- strip 850 (post #2625994), strip 1264 (post #3459472), and an as-yet untranslated strip (so I don't know the number), post #3546790 . The other girls (plus Yumeko) are in the second, too, and Ai recurs in the third (though it's pretty much a cameo for them both).
Updated
Yes! ... One two,Everyone...!Let's go! ... One, two! EI EI OOOOOOU!!
EI EI OOO ~!!!
Oops~Oh my~♪Waaa~!...Ai-chan, your voice is too loud.Aaaa!! My mistake!! It's always like this!No... Please don't hold back... I'll also yell... with all I have... !It's better if we save our energy for now...Alright~ We have received a very joyful 'Eieiou'~Indeed! To step forward with our all is our way of doing things!Then one more time! No holding back, okay!?...Told you...but as we are still doing mic checks, please keep it down, thank you~
Mic test, mic test~
Cinderella Girls Theater
劇場第818『セーブしないよー!』
Theater Episode 818 - I always go all out—!Then, Kyoko, if you will!