As part of repaying his debt he feels he owes her, Rei wants to help Hina in anyway he can, and that means getting a new perspective on the matter of bullying. Hayashida-sensei misunderstands at first. Rei isn’t the one being bullied. Indeed, he proudly proclaims his hard-won and long-standing invisibility at school.
When he brings up Hina, then describes her personality in such great detail and then presents his passion and motivation on the matter (“my duty as a human being” and such) Hayashida starts thinking that there is someone Rei likes. Of course, Rei isn’t thinking that way at all; Hina is not just a dear friend, but close to family, and his lifesaver to boot.
Hayashida gives Rei some good advice, including to tread carefully and not make a big fuss at school, lest it just make things worse for the victim, but to instead listen very intently to her feelings on the matter; how she’d like the matter resolved.
You know Rei is super-serious about this endeavor because he has a back-up plan: if Hina has to change schools or get a private tutor, he means to support her, not just emotionally, but financially. To that end, Hayashida spots a stack of shogi tournaments into which Rei has entered, calculating all of the winnings he’ll amass, which makes him a bit worried.
Despite saying he (literally!) can’t afford to lose again, he does inevitably lose, and is so angry he wrangles an all-to-willing Nikaidou to strenuously train with him. Nikaidou thinks Rei finally has fire in his belly and is utilizing his Best Friend; Rei just wants money to repay Hina!
The next day, Rei helps Akari lug home a whole mess of groceries she got a big sale. When Rei tells Akari his weight, she hurries home to start cooking, and won’t hear of Rei leaving.
There’s something about Rei, perhaps in part his personality; and the experiences he’s had (the loss of loved ones being something they share), that has Kawamotos pour their hearts out at him. Akari feels she can talk to him, and criticizes herself for the job she’s done as surrogate mom to Hina, lamenting she’s “no good.”
Only nineteen herself when their mother died, Akari had barely lived any life before suddenly becoming a mother of two. She did her best, but in hindsight worries she instilled “ham-fisted” ideals into Hina, which led to her predicament with her friend and the bullies.
Akari admired Gramps simply praising Hina’s courage, but she hates the part of herself for wanting Hina to simply run away rather than do something that would cause her to be unhappy or alone. This is, of course, silly; Gramps has lived a long-ass life, of course he’s going to have more wisdom on these kinds of things. Akari is too hard on herself here.
Rei reassures Akari that just as Hina did nothing wrong in fighting the good fight, neither did Akari. After all, Akari raised the girl who saved Rei’s life; that makes Akari his savior too. Had Hina been raised not to be as kind as she is, or to think of herself before others, Rei might not even be there talking to her.
His honest words cheer Akari up, and she fixes a big ‘ol pot of curry for dinner. When Gramps returns from the theme park with Hina and Momo, he complains that Rei is there “again”, but he’s only joking around, and orders him to sit, eat, and stop making him feel like the bad guy.
While stepping back into the house, Hina hands him a cartoon cat phone strap that somewhat resembles him, as thanks for everything he’s done. Hina expects Rei to think it childish, but he tells her he’s moved, and thanks her. It’s such a nice, quiet, warm moment shared between two people who will hopefully be thanking each other for being there for one another for a good long time to come.