Why the heck is this comment section complaining again?
Before complaining shallow comments like, we see this in shounen manga, understand the scene first.
First off, this is completely in Kariu's character to shout. After seeing progress and seeing Kaizaki run away, something he specifically told her not to, she's reaching her limit. He's being hypocritical of himself AND suddenly not trying to interact with them. Especially after he's done so much for him, seeing his behavior like this, any of his friends would be worried. After she finally confronts him, she still sees him somehow avoiding and running away, and knowing Kariu, this pissed her off to no end. She's angry at how he's acting and how he's not following his own advice. Why the heck is he not enjoying himself and trying to suffer?! Even after all he's done to gather everyone together so they can live life to the fullest, why is he the only one who's not?
This also makes Kaizaki show that even despite not remaining in their memories which caused his downward spiral of despair, that this effects that he's made on them will remain. He was so focused on one aspect of the results (kind of like Hishiro in the past and beginning of this arc) that he didn't think the middle and the other part of the results. That even if they don't remember, the fact that he's done it and changed them for the better does not change. And Kariu yelling this to him because he himself doesn't seem to understand this simple fact that he's helped them so much and she's yelling because she's (nor others) not happy with the outcome, he feels wanted. He feels that despite all of this, he's still an essential part of their lives, whether he remains or not.
And to Kaizaki who's been so important to let them figure this out and helped them, he truly needed that dose of medicine for himself. And why his words can come bite back to him so easily, why the cast was able to reiterate his words back to him. So he can get out of his self-sacrificial shell, this mindset that he'll just disappear from their lives and it wouldn't matter, when in fact that's the furthest from the truth. This was basically his turning point that he can move on from his past self, he can stay for good and enjoy this experiment to the very end, without having to hold back.
So why are people complaining for shallow reasons that it resembles a shounen manga? In my humble opinion, this scene is way better than what any typical shounen manga can achieve. Stop comparing them when they don't even have anything in common.