Qing Su's Links
Saki is Qing Su's calm counterpart. Where Qing Su is chaotic, Saki is much more docile. The two are often seen around each other, and Qing Su considers herself to be Saki's "shell-breaker" and mentor.
Eri and Qing Su are friends, though they have more of a rivalry than anything. They're both the most out-there idols, though Eri takes the cake in terms of appearance.