This is a "Wild Mass Guess" entry, where we pull out all the sanity stops on theorizing. The regular entry on this topic is elsewhere. Please see this programme note.
Tokurei Sochi Dantai Stella Jogakuin Koutouka C 3 Bu
Sonora is afraid Yura is going to end up like Rin.
Yura's attitude before and during the twenty-four-hour tournament suggests that she's slowly turning into an airsoft tryhard. This is made all the more significant with Sonora's last words of advice to "always have fun", which Yura has tragically forgotten in her efforts to exact revenge against Rin. All of this comes to a boiling point at the final leg of the twenty-four-hour tournament, when Yura zombiesnote continuing to shoot after being hit, which disqualifies one's entire team by tournament rules in order to shoot Rin and win the tournament, an act that she is regretting, and will have trouble living down.
Pretty much confirmed by episode 9. Yura has, in fact, became almost exactly like Rin, so she quits C3; and appears to have joined Rin's crew, if the next-episode preview is anything to go by.