Nah he's the moody taundere that Murata likes and Kousaka is Sunakawa's friend. What happened on the latest chap is that Murata went with Kousaka to his place cuz Kou offered help to Mu(from chap 2) since he knows almost nothing about the gay world and Sunakawa. So as Mu went with Kou, Sunakawa was wondering why Mu isn't contacting him anymore and reminiscing his high school with his "friend". Now while walking he heard Mu's friends are talking about him(Mu) going somewhere with somebody which is Kou. As soon as they mentioned Kou, Su was pissed and asked them if they know Kou whom they don't know much. Back to Kou and Mu, they're inside Kou's place, talking about Su, Mu's sexuality(which he's new to), and if Mu was grossed out by gay sex(which he isn't and he even wants to learn more about it). So Kou started his move making sure Mu is really attracted to men, licking Mu's nipples but they're interrupted by Su's banging and shouting on the door. Su barged in, Mu fixing himself, flustered and Kou still with his cocky face. Kou looked to Mu saying that it's consensual, Su asks if it's true but Mu answered stuttering a no. Then Su took Mu out shutting the door and went back to Kou asking Kou about what he did, teasing and causing a misunderstanding for Su and Mu, the guys that liked him(Kou) before and people around him(Kou) that gets along. Kou answered saying if Su knew he's like that then why didn't Su cut ties with him and Su is the one who's using him since he's the only gay(he can talk and relate to) that Su knows. Then Kou made him flustered saying that Mu seems to be his(Su) type and that made him act all tsundere then walks out surprising Mu that's waiting outside. Mu apologized that made him(Su) more pissed since Mu doesn't even know what Su is mad of. Then Su pondered if what is he even mad about and if what Kou and Mu did is consensual.
Sorry for the long read (⌒▽⌒)
Also Kousaka has the same name as Murata's ex
no no it's fine thank you for detailing it up! i just genuinely suck at remembering names also i see :0 makes sense now
what the hell were they talking about... my head hurt trying to decipher everything sunakawa (is that the 3rd party's name?) said