I super, super loved this one. Apparently it was actually supposed to be the end of the "series" for these two, but Natsume asked to continue it, so we'll see how the rest goes. It's interesting because the main characters got together in volume 1, so unless there's (heaven forbid) some breakup plotlines, the whole series should really be about two adults navigating their complicated lives and stressful careers while being in a committed relationship - which is something I love, and pretty different from what you normally see.
It almost feels like there's a bit of a time skip between these volumes...which I think is true later on (Onoe mentions that they've been working together for a year, although I'm not sure how long it took them to start dating), but in the first chapter, they'd just gotten together the week prior. They hadn't technically talked about what their relationship was, but I was pleased to see that Onoe was already treating it as something completely normal. He was irritated that Kaburagi wasn't being nicer to him, but there's no real sense of insecurity - he knows Kaburagi cares about him, and any of his jealousy pangs are about Kaburagi's past.
For instance, when Kaburagi finally invites Onoe over to his place, Onoe sees his gigantic bed and starts thinking about how Kaburagi used to not have a problem with a bunch of totally casual relationships. Past tense: he's not concerned in the slightest that this is something Kaburagi's still doing, or thinking about, now that they're together. I hope things stay like this, because it's really refreshing to have characters who trust and talk to each other.
And communication really is a big theme in this volume. Onoe is a loud, overexcited spazz, but he's actually really thoughtful and mature, and a lot of this comes out in his interactions with Kaburagi's little sister. I loved that entire storyline, too; there was no dumb misunderstanding or jealousy, and it really felt like Onoe had immediately adopted Nori as his little sister, too. While he enjoyed bonding with her and complaining about Kaburagi, he ultimately refused to do anything that would actually hurt Kaburagi, and he tried to smooth things out between the two of them as quickly as he could. It was just really nicely handled.
There is some miscommunication later on, and some teary heartbreak, but Onoe keeps pushing for the whole "if we don't talk about it how can we move past this?" and Kaburagi doesn't ice him out for all that long. I love that the conflict here basically boils down to both of them trying to protect each other - and Kaburagi starting to realize that while Onoe is a good person, it's not because he's "innocent" or pure or naive; he's seen the dark sides of the world and the people in it, and he's choosing to remain kind and optimistic. Kaburagi doesn't have to shield him from the dirty parts of their job.
I also really like Onoe's friendship with his old classmate and longsuffering bartender. I wonder if Masa-Yan and Nori will wind up together? That would be cute.