Yeah, I don't really get Sachi. This group managed to hold together for 3? years and then it blows up over some arcade otaku and Mr. Chin. Seemed like she was trying to rein things in on page 10, but then in the next two pages she just goes nuclear. Like somewhere between 10 and 11 she decided to give up on everything and live out the rest of high school alone.
I guess there was some kinda rule that you can't shittalk people behind their back right in front of them. That seems to be consistent in the previous chapters.
So Sachi is shitting on the otaku, but Minami unexpectedly took up their defense. The conversation turns on Minami so Sachi tries to bring it to a halt. But Minami's autopilot was set to crash and burn as usual. Once Mr. Chin is brought up, things are unsalvageable so Sachi slams the throttle and crashes this train (with no survivors).