Man, the friendship between Yuzuki and Makoto is just the most heartwarming shit! The whole girl squad was really wholesome this week actually, with Mika now firmly part of it. And we even seem to have Shima take his first steps to reconnect with his familiy.
But of course Ririka has to show up to stir some shit. That glance between her and Shima's mother at the end does not bode well. They obviously recognized each other and were both pretty shocked. It'll be very interesting how this plays out next week, with Shima possibly between the front lines.
Edit: I just saw on MAL that Ririka is voiced by Minako Kotobuki (Mugi in K-On). With Aki Toyosaki (Yui) voicing the teacher, that's two of the K-On girls' VAs reunited in this show. Not really relevant, but I like spotting connections like that. Well, they are both really talented and versatile VAs, so it's not that surprising that they'd get a large number of roles.