Kaz finds Majima's devotion to his work impressive, and his devotion to his brother even more so. He doesn't seem to take much time off though? But hey, he likes baseball and he's a really hard worker, so Kiryu really admires him and considers him a close friend. The two of them became fast friends thanks to their mutual love of karaoke, cheap drinks, and the fact that Kiryu spends several nights a week in his club. I mean, Majima saved him from a giant squirrel and help Kaz remember how to fight. He's great. They both kind of kept hanging out until it was painfully obvious that they had feelings for each other and have been dating since mid-June. With Majima losing an eye and being so prevalent in Kiryu's memories, there's no doubt in Kiryu's mind that they were meant to be together. And fight each other. Because that's the kind of thing they both find hot.
Makoto's a good kid with a strong heart who Kaz hopes will find his way one day... in the meantime he's his baby cousin who needs looking out for, and he's the guy to do it. Plus his mom makes amazing ramen. Makoto trusts Kaz a lot and that trust is shared just as well. Really, Kaz just wants to see Makoto be happy. Poor kid needs to chill out a little.
Now that Kaz has properly met Yuuri, he likes to keep in touch with her and is fiercely protective of her (even if she might not necessarily know it?) He has an open invitation from her uncle to stop by on weekends and have dinner with them, which he really appreciates. Yuuri's a sweet girl who has a really cute cat and Kiryu would die for her.
An excitable young girl who mooches off Kaz's generosity. Kaz doesn't mind of course, he just likes being a positive influence with kids. She seems especially bright and committed to helping people, which just makes Kaz want to care for her more. She is also close with Majima, which has made interactions between the three of them feel almost... domestic. It's soo cute. Kaz likes to help her with her homework and will put up with any of her antics because she's on the same page as they are when it comes to a lot of things. He loves her and he would use all of his power to make sure she never once has to suffer any kind of hardship because Mafuyu is flawless.
A kind homeless guy who works at Inkwell and likes cup noodles. Also shares Kaz's view wrt crime being ok sometimes. He's a good dude. Yato is cousins with Mafuyu and lately Kaz has found himself forgetting him at times... very weird. At the very least, he's a fun guy to be around and Kiryu is going to try to keep from forgetting him.
A kid who has a bad habit of stealing and causing trouble. He's good at heart tho, Kiryu believes in him and is glad to be there to pay up for the things he steals. Maybe one day he'll stop, who knows. He's got a passion for photography and often sends Kaz pictures of cats and other things like that. Yukine also gave Kaz a digital picture frame with the selfies they took together at prom. It's the cutest thing ever. (Chance of adoption: HIGH.)
A fellow white collar worker who frequents a lot of the same clubs Kiryu does. He's Majima's accountant as well. Miller has been trying to help Kiryu learn to cook, emailing him recipes and coming to his place on occasion to try and show him how it's done. It hasn't really stuck, but Kiryu appreciates it all the same. These two are pals but on top of everything, Miller truly trusts Kiryu. He confided in him about his family's history of alzheimer's, and trusted Kiryu to make sure that if he ever forgets Retrospec, it's the app and not a deeper problem. Nothing is more important than a promise between men.
A kind guy who gave Kaz an open invite to his place for weekend potlucks and free cookies. They met after Kaz gave Fai his spare umbrella. He's been hugely supportive of Kaz and Majima's relationship and a good friend in every sense. They're still due for a double date one of these days, Kaz hasn't met his boyfriend yet...
An extremely friendly drag queen who treated Kaz to a really nice date. Kaz didn't realize he was in drag at the time, but finding out didn't make any difference to him. Jirou is just very, very pretty. Also super loaded? Kaz might get some clients through his parents' connections. Nice.
An old friend of Majima's who works for the CSI of the Recolle PD. Kaz actually first met him because his job sounded cool. Very Torts & Tribulations. It wasn't until later that he found out that Tatsuo was an orphan who grew up alongside Majima. He's a good guy. After his apartment burned down, Kaz offered to let him stay at his place and the two grew much closer then. He's since moved out (with Kiryu's help,) but they're bros for life now. Once you share Cherry Garcia, that's it.