Starting to see more of the anime restructuring here; they pretty much moved things around to make the rings the conclusion, with all the drama leading up to that. That makes sense if you want to wrap up a story with a satisfying ending. (Unlike a lot of shoujo anime, that just faithfully reproduces the manga and then stops in an early arc of the story and you never find out what's happening next unless you go buy 382 books.)
In reality, the rings are a major part of the drama - in this volume, at least. And boy is it dramatic.
I'm actually loving everything about Setagawa and Kousuke's relationship. One of my other big worries/impressions about anime vs manga was that they'd really play up the top/bottom dynamic and have Kousuke be really pushy and overbearing. But he's not at all. He's got a big, messy, nose-in-everyone's-business personality, but he cares so much about Setagawa and takes cues from him a good amount of the time. The manga isn't very explicit, but it does make it clear that Kousuke is always checking in with him, ready to back off or shift what they're doing if Setagawa's not feeling it, and he insists on Setagawa taking the lead a lot, in directing how they do things etc.
What Setagawa says at the end of volume 3 (during the ring exchange scene in the anime as well) kind of carries a different meaning in the manga, because you see how very imperfect Kousuke is. He's not a hero. He's not a god of destruction. He's just some guy, trying to make his way in the world like everyone else, and not always succeeding at it. And Setagawa loves him even more for that.
Initially, Setagawa admired Kousuke and wanted to be like him; that's how everything started. That's the whole point of the story, really. He grew up with a single alcoholic mom who works at a hostess club and then drinks all night, draining the paycheck she'd just earned, at a host club. I forget what manga I'd read recently that explained this is pretty common (or maybe I was just looking it up online?); apparently, a pretty big percentage of host club profits come from hostesses showing up to drink and hang out after their shifts are done. Money in, money back out.
That's why Setagawa lives in a dingy apartment where he handles all the cleaning, cooking, and probably the bill-paying at this point. He's going to school full time and working a part time job, while his mom racks up debt at the host club and then "borrows" money from her son to pay it off. She's open about this while she's drinking, so the hosts know about it and don't feel great about their role in her debt and what she's doing to her son.
One of the guys shows up at Natsuo's bar early in this volume to talk about how much it bothers him to be watching her draining her life away like that - fully aware of what she's doing but unable to stop herself. He's just doing his job, but he's still struggling with some guilt over contributing to the problem. Natsuo doesn't really pay attention; he's a bartender who hears lots of people's problems, and the only one he seems to actually care about is Kousuke.
(I do wonder how much further the manga will take the hints that he's in love with Kousuke; apparently he's been friends with Kousuke the longest, but I don't know if they have History or if it's always been silent one-sided longing, like when he starts to touch Kousuke's hair at the end of this volume, pulling back when Setagawa barges in to retrieve him.)
All the stuff with Setagawa's mom is really, really dark. This volume opens on a pretty stark note: I don't know what the deal is with his dad or if we'll ever meet him, but he'd at least abandoned them, and possibly done worse. It's also indicated that some of her later boyfriends hit her, and possibly Setagawa as well. All her friends tell Setagawa, who's probably at this point in elementary school, that he's the man of the house and has to take care of his mom. It's a big part of what made him grow up so fast, becoming mentally and emotionally responsible in a way his school friends just aren't, because they never had to figure out how to be independent and survive without their families' support.
Setagawa's question - who's going to protect me? - never really gets a solid answer. Because all that weight falls back on his shoulders. By the point this series starts, he doesn't know how to rely on anyone else. He's never had anyone else and can't trust other people to do anything for him.
That's why the entire Ohshiba family is so incredibly important to him. It's not just Kousuke. It's having a house that's clean and warm and fully stocked with food and other necessities, and people who pitch in to help with meals and chores and sit around the table and tease and joke and talk to each other. That's the life Setagawa wants. And he's completely terrified of losing it again, and being unable to cope with his dingy real life once he's had a taste of what's possible.
He's so, so incredibly happy throughout this volume, and that's why when things come crashing down they hit him super hard, and he reacts more strongly than he needed to.
It's not Kousuke who causes the drama; it's Setagawa's mom.
She comes home and rummages around in Setagawa's wallet when he's sleeping after work, looking for his latest paycheck so she can pay off the host club people who're hounding her about her debt. He's a part timer so he doesn't have nearly enough money to cover her bills, but she does find the ring he'd put in there for safekeeping. And being the deeply selfish person that she is, she immediately decides that she'll pawn it for some extra cash.
And that is a bridge too far for Setagawa. He's spent his whole life taking care of his mom, letting her take everything from him and trying his best to be a good, dutiful son who doesn't cause anyone else problems, but seeing her taking away what's basically his engagement ring is too much. He sees red, and he snaps.
This is actually a pretty brutal volume, but told really effectively. The "you can't be his hero, Kousuke" exchange at the bar makes more sense here than in the anime, when it was simply about whether to keep dating. Natsuo's basically telling Kousuke that he can't date and rescue someone whose life is this messed up. Kousuke's a meddler who always wants to help people; that's why he became a teacher, and why he got that "Bear Killer" nickname from wandering the streets trying to help thugs. But Setagawa's family life has some pretty intense ingrained problems that an outside party can't just sweep in and fix - and maybe shouldn't, or at least in Natsuo's eyes, because then it just shifts responsibility and makes Setagawa rely too heavily on someone else. Then if that support's ever removed, he'd fall and shatter to pieces.
That's what Setagawa's worried about, too, but has never expressed to Kousuke himself. He's trying too hard to handle everything on his own, like he always has. As much as he's started to open up in other ways, this is still a piece of him he's afraid to show to other people.
So when he gets in the fight with his mom, he doesn't go to Kousuke, whose opinion and love matter most to him. He goes to Hasekura's house and sits on the floor all night, not even speaking to him, but just needing a place he can hide out for a while.
Fortunately, Hasekura pulls in Ken, who calls Kousuke to tell him where Setagawa is and that he's safe, because Setagawa does have a pretty big support system at this point. Even Shige was ready to open up his home to him.
But Setagawa's just steeped in self-hatred at this point, because as Kousuke finds out when he goes to talk to Setagawa's mom, he'd hit her in the process of trying to yank his precious ring back from her. It's not shown, so it's unclear if he hit her directly or was just too forceful and knocked her over, making her hit her head on something, but either way, he despises himself for it. He's not that kind of person. In the previous volume, he knocked Shige gently on the head as his "return punch" because he's just not the kind of guy who'd ever get physical with someone, no matter how upset or angry he is.
Except...he did. With his mom. And he's horrified with himself and unwilling to tell Kousuke or to have any of this taint the one good, perfect thing he had in his life: his relationship with Kousuke (what the ring stood for) and the entire Ohshiba family's warmth and love.
This volume is actually kept pretty short, cutting off with Setagawa going to get Kousuke from the bar, after which they'll presumably talk about things. There are a couple longish bonus chapters after, including one with the Chairman's crush developing a girl crush on Hasekura's older sister - I winced going into that but it's a surprisingly heartfelt story about appearances and sexist beauty standards and possibly even female friendships.
In short, this whole series is a lot more thoughtful and deep than I've been thinking all these years. It isn't just ooooh age gap, kinky - where I'd kind of unfairly slotted the manga in my head. It's handling a lot of tough, complicated topics with a lot of grace and a heavy emphasis on friendships and family.