Except in Chaptrr 37 when he first goes to the club room Hazuki uses a lot of the same language when she initially recruits Kurose. She makes it clear the intention is that he play at the school festival, tha they need a guitar player for her to make the right music for it, that it's thr bassist's last year to play, and that the last guitarist quit because of the very same high expectations. Kurose should have been triggered then at least shown a ton more reluctance (with baby flashbacks) than he did in that moment instead of more or less agreeing by flexing his skills and agreeing to practice with them provisionally while they all arranged music around him assuming he'd be performing with them. The idea that he was only playing for fun is not seriously believable- they made it very clear they were pinning their hopes on him performing, and the first thing he thinks in his head thr next chapter is "the cultural festival is only a few weeks away...I gotta practice harder!" which sounds very much like someone expecting and motivated to perform and very much not thr thoughts of someone with past performance based trauma making them afraid.
Screw it, I'll bite.
Ch. 37:
Kurino-senpai: "Even if you don't join officially, it'd help a ton if you supported us just for the school festival"
Kurose: "Is it okay if I just joined practice as a helper first? I've never been in a band before and I'm still not very confident."
Hazuki: "Of course! You've been keeping the fact you play guitar a secret, so what made you decide to do this?"
Kurose: "I just want to help someone when they're in trouble. That's all there is to it." (see ch. 21 for confirmation that Kurose is a busy-body who will sacrifice himself to help others.)
Ch 41:
Hazuki: "And now with you helping us out...I'm so happy we get to play together as 'Watmelo'!! I'm so glad we got you to be our guitarist, Kurose!"
Kurose's Trauma: "We never should have left it to you in the first place, JUST STAY OUT OF IT!"
Ch. 37: "You can join as a helper! That's fine!"
Ch. 37: "You like to help people? Then we're counting on you [as a helper]!"
Ch. 41: "You are our guitarist and the reason we can finally play together!"
~~One of these things is not like the others~~
~~One of these things doesn't belong~~
~~Can you tell which thing is not like the others~~
~~By the time I finish my song?~~