When Raidou is feeling under the weather one day, he just happens to resemble the love interest in a shoujo romance novel. We know Aharen to be sensitive to how Raidou looks at her, especially after their tender moment at the fireworks festival, so his misleadingly amorous face is almost more than she can take. As for Raidou, he passes out from his fever and goes home early.
The next day Raidou is fully recovered (as one would expect of one with such a hardy build as him), but Aharen is out sick. He’s asked to deliver printouts to Aharen (a time-tested but by now obselete practice in the ageof the internet) and ends up encountering a third member of the Aharen clan: Reina’s much taller little sister, Eru (Hidaka Rina).
Eru exhibits certain tsundere qualities, treating Raidou with initial hostility but later admitting to her sister that she finds him “interesting” and “doesn’t dislike him”. She also has somewhat extreme notions of cooking what with bringing a whole tuna home and cutting it up with what could only be a katana.
Reina is very grateful Raidou came by, but he doesn’t impose further on the Aharens by staying for dinner. Eru watches as her big sister clings to him. While bathing with Ren, Eru admits that she suspects Reina to have “special feelings” for Raidou, but whether they’re actually going out remains a mystery to her.
Lil’ Ren sets out on a shopping trip and runs into Raidou, perhaps for the very purpose of finding out for sure whether he’s dating his big sis. When Ren realizes he’s lost his wallet and all the money for the groceries he intends to buy in order to help his sisters out, Raidou produces his wallet, only to find it’s empty too.
Thankfully, the Aharen dog Nui produces Ren’s wallet with the cash needed, but before Eru can get a straight answer out of Raidou about his relationship with Reina, Reina appears, and the discussion is tabled for now. Sure enough, in the presence of two Aharens Raidou effortlessly calls Reina by her first name, making her steam and blush.
Maybe there’s nothing Raidou could say to Ren or other curious parties to satisfy them. Maybe he and Reina simply defy specific labels.