Satoko doesn't know what to do with herself after Rika leaves for St. Lucia.
They only lived together for a few years, but she can barely remember a time when they didn't greet each other at school every morning and walk home together every afternoon. Now they can only see each other on weekends, and not even every week.
She's quiet at school, and everyone gives her space instead of pushing. It feels like how they all walked on eggshells around her when her uncle was around, and she hates it. But at the same time, it's what she wants—for everyone to just leave her alone.
Shion comments on how she's clearly at the "depression" part of the five stages of grief, and the others nod and agree. She doesn't bother to correct them, but they're wrong—she's not depressed, she's angry. Angry at the world for never giving her a break, and angry at Rika for abandoning her after everything they've been through.
Well, whatever. If Rika wants to throw away their life together so she can go to a fancy boarding school, so be it. She can make her own choices, after all. They aren't children anymore.