Souta’s little sister Nazuna is working at the restaurant. This leads to a discussion with Izumi the next morning where Nazuna ends up falsly believing that Souta is dating Poplar (and that she’s in elementary school). Distraught, Izumi goes off on a “journey” where she runs into Mahiru. Mahiru tries to cheer her up while finding Izumi’s reliance and obsession with her brother (not knowing it’s Souta, of course) a little weird.
I’m not sure if this is a start of some new arc where Izumi tries to run interference with Souta’s alleged relationship with Poplar the not-really-in-elementary girl or if it was a one-off episode, considering it takes her days to practically craw from one room to another.
In any case, the Izumi stuff was OK. Her conversation with Mahiru was funny, but the rest was just kinda blah I thought. On the other hand, Nazuna is always entertaining and is still definitely my favorite non-regular character in the series. I would be just fine if she just showed up in every episode.