Yeah, it was pretty obvious. Itadori just nods, growing a bit more serious. "Yeah. Did you happen to see anything or anyone that could be responsible?" He lifts the little curse he's holding up to eye level. "Since you can see these."

“Um.”

Okay so on one hand, yes he definitely did, and probably should tell the strange loud insane person with magic, but on the other hand: Mahito is terrifying and could very easily do the same thing to Junpei, too, and furthermore he’s like, a baby born from evil spite magic who’s trying to figure out how to person. Probably when there is a baby you should… not immediately throw it to the baby police. Except, you know, the murders. The admittedly probably justified murders, considering the victims, but still.

“I feel like you know the answer to this question already, and you’re seeing how I answer it, which makes me want to shrink into an unhelpful witness ball who hides behind a lawyer that I don’t actually have, and actually did you set up the curse showing up to see if I would see it??”

Blink blink. "Did I mention I like you? Um, sorry about the unhelpful witness ball. I wasn't personally the one who set the curse," another opportunity for Yoshino to react, but Itadori thinks he won't, "there but I was part of the plan, yeah. If you couldn't see it then no foul, I'd get it later; if you could see it and could kill it then we have an unknown curse user; and if you could see it and didn't kill it—well, here we are. Didn't count on the teacher, though." Sigh. "Ijichi-san should really learn to think before he does things, and look before he thinks." He gives the curse a squeeze and it squeaks like a toy. "This one is harmless, the worst it can do is make you have a bad day, maybe a headache or your pencil breaks or your lunch bag leaks into your backpack or something like that."

He looks at the curse dubiously. See, those things sound minor, but they can also help add up to a greater whole that is definitely not harmless.

“… could see, couldn’t do anything about,” he says very quietly. “I-I‘ve seen them for, um, months now? But I don’t have any cool magic powers or anything. So.”

Now here's the nearby river! Itadori takes the steps down towards its grassy bank, folding his arms heedless of the protests by the curse. "Well. I'm sorry you had to witness—that. At the theater. It looked awful, even if the kids themselves were awful too."

"Oh. Uh. Thanks. Er. How'd you know, did you do, uh. Research and stuff?"

...hmmm. Yoshino didn't seem to react to the word "curses" the first time, but it looked like he'd been nerdsniped, and the word "sorcerer" did get a reaction. But then he said he did see—no, he did know who or what did that to the other kids.

But is Jujutsu High even a proper secret? Every jujutsu sorcerer knows about it, every curse user worth their salt does, too, and everyone who isn't worth their salt is no threat.

"Yeah. Those three weren't the first. Or the last. I'm, uh, with a group of people looking into it. You're the only actual witness we've found, so far."

"Oh," says Junpei, softly. Wondering.... why that is.

".... what were the other victims like? Was it the same sort of, of. Was it people like them."

"...no. No it wasn't—the school records weren't that clear about what they were like but I read between the lines—no, it wasn't all horrible bullies with no empathy."

"But I mean—how can you be sure? You read between the lines on the school records, but, but. ... I think a lot of people miss how shitty people can be."

"I... know. But..." How to phrase this. "Those horrible fucks, I've met them before. Not them, them, but, people like them. You know? And," you don't need to be a genius, talk to Yoshino for five minutes and you know exactly how cruel those kids were, "I'm not really sure how to say this in a way you'll believe me. Most people aren't like them. And I'm not saying everyone else, who never did anything about it, are saints or anything. But the kind of shit those kids did, the kind of, of petty cruelty—most people aren't like that." He runs a hand through his hair and then walks over to the bottom step of the stairs leading to the riverbank to sit down. "Most people are just sort of—they don't think much about these things, they see you being bullied and they convince themselves it's not that bad, and it's not their problem anyway. The teachers, they create a story where it can't be very bad because if it was very bad then it would be their fault for not catching it sooner. And most people want to believe they're good, but that narrative doesn't survive if they let themselves really see the kind of horrible things that happen right under their noses.

"And all this is to say, I don't know if the other victims were great people. Probably not. But they probably weren't horrible like your bullies, because very few people actually get that bad. And the important thing is—whoever, or whatever did this, is not looking specifically for bad people to kill." Not that killing bad people is good, but he's not about to discuss the sanctity of the life of the people who probably made Yoshino thinks his own life isn't worth living at times. "It's random people. It's this fifty-something lady who lived alone and had no children, it's a police officer who was at the wrong place, it's—" He swallows, dryly, and shakes his head a bit. "It's a group of ten-year-olds who were chasing a ball they accidentally kicked into an alley while playing with it in the nearby playground."

"Those are. Direct, actual examples, not. Metaphorical?"

"...yeah."

"... Then I have no idea why I'm alive," mutters Junpei.

He looks up, again, at Yoshino. "Can you tell me? Who or what it was?"

"Um." This is totally going to get him killed, isn't it. He's the extra in a horror movie, a dead guy walking.

But he won't be a stupid one.

"... Creepy stitched curse person. Grey hair, pale skin, eyes two different colors. Uh. Hangs out in the sewers. Can carry on a perfectly polite conversation. Explained some things about magic to me."

"...okay. I—curses don't usually—can't usually carry conversations. So most likely a curse user..."

"No. Definitely a curse. Invisible to other people, and there was the, the. ... Curses have an, an aura? All of them? Like they're badness incarnate. And it was big.”

Blink. "But—then—a curse that can converse—not even the special grade I fought—Yoshino-san, this is incredibly serious—" The only curses he knows of that can talk like that are volcano head and Sukuna, so if this curse is at that level...

He reaches into a pocket to grab his phone but drops it at a sudden tremour.

Junpei shrinks a little and gives a small whine. It's probably a coincidence but maybe it's not and maybe he just pissed something off.

"D-do they all have to be bad, though? He, they? It? seemed, uh. New. Experimenting."

"The... I only know of two other courses that can talk; one tried to kill my Sensei, and the other was the one that killed me. And... he did it for fun. Just to make my friends suffer." He shakes his head and reaches down for his phone again to call Ijichi. "Curses are formed out of the negative emotions of humans. But so is jujutsu sorcery. So I—don't want to declare that it is impossible for a curse to exist who isn't evil. But... if so then this one will need to be taught some manners."

He frowns and looks at his phone, then tries dialling again. "—sorry, I forgot to say earlier, but, uh, given that you have the ability to see them you probably have the ability to do jujutsu sorcery, yourself, and I think my organisation would really like to help you learn how to use it."

"Um. Okay. But... um." Wince. "I'd feel really bad about turning the first person that was nice to me for no reason in to the authorities, so, um. ... Please try to be nice?"

"...yeah. Okay." He looks at his phone in frustration again. "What is Ijichi-san doing." Sigh. "Well, nothing to it. Does this curse know where you live? Do you have any family it—they—could hurt or threaten?"

"Uh, I don't think so? But maybe. And, um. ... My mom."

"Hmm." He closes his eyes and thinks. What's the next plot beat in this story? The curse could actually be a good person, or, well, a confused person anyway, and the story goes in the direction of humanising curses. Or it's actually very evil and trying to manipulate Yoshino for... what reasons? Fun is one possibility; Sukuna's sadism is not atypical for the kind, and a powerful smart curse wouldn't really need someone who has no training, not without spending a lot of effort doing that training. Or maybe Yoshino is bait? Trying to pull at their—his—heartstrings, and damn it if that was the ploy it was working, Itadori could feel himself caring for the boy and wanting to, to avert whatever horrible fate this story wanted to inflict on him—

—this is real life. It may be operating on story logic but story logic needs to still go through regular logic.

He can't reach Ijichi. So what are his options? He shouldn't leave Yoshino alone, not without checking in with the grown-ups (even though the grown-ups tried to have him killed... well, it was different grown-ups). So either he follows Yoshino or Yoshino follows him. If they go to Yoshino's place then the curse could be following them and he isn't skilled enough yet to hide his own cursed trail—

—no, damnit, he visited Yoshino's porch, that ship has sailed. But he didn't know it was this bad, at the time, a talking curse was just out of anything they'd considered. Therewas Sukuna, and volcano-head, and while Gojō-sensei is much more powerful than the latter and claims to be more powerful than the former, there's only one of him.

So given that his own cursed trail is already there, there would be no additional harm in following Yoshino to his place, and maybe placing some protections there. He definitely needs to talk to Gojō-sensei, though.