The Masque of Purple Death

I imagine though that gojo tries talking to him similar to geto. Things go... a bit differently compared to what happened then, nanami revealing to him that hes not against jujutsu society as a whole, just the way its run. After that bombshell, gojo tries every encounter they get (i imagine they have a lot of those thanks to the higher ups sending him to hunt nanami down) to get him to stop his murderizing ways and find a different way. He keeps failing, but nanami always assures him that hes on gojos side as he wants to reform and help their society

I can actually see him helping subtly with getos defection. Since hes a merc and sorcerer for hire, i can see gojo hiring him to do things he cant since hes always stretched too thin. Like keeping tabs on geto, sabotaging his efforts to collect more curses, etc etc. Ofc he still murderizes people and other targets though, he might be a bit of a jujutsu vigilante but hes still a blade for hire

I realize that ive just turned nanami into Jason Todd Red Hood.

ANYWAYS--

With Kento being outside interference wholly focused on helping gojo and doing his own thing, id like to think theres a good chance they could stop the Night Parade from happening. With his time working in that profession, i imagine that he develops his technique much further and has a more thorough understanding of the other aspects of jujutsu like barriers, and simple domains. Add to that his lack of a moral code and shit about murderizing people, and i genuinely think that theres a good chance of it either not being as bad as in canon or just. Straight up Not Happening. The Night Parade, i mean.

I can see nanami, after learning of what getos planning, coming in and systematically dismantling each and every one of his plans via murder. And gojo would trust him, since i imagine at this point, nanamis serving as his eyes and ears on geto, and nanamis been helping him deal with all the troubles hes been causing. So ofc, while none the wiser on as to how nanamis gonna do it, he trusts nanami to execute on his plan.

So off he goes, eliminating or killing curse users that might join geto, defeating or at least weakening higher grade curses that geto might have his eye on, and systematically eliminating getos different cult strong posts via murdering important members and whatever of getos inner circle he can reach. At a certain point, i can see geto getting wind of what nanamis doing or at least realize that nanamis the one behind the fuckery happening with his plans. I see him being... unsure on whether or not to be furious or amused, and a bit more research later, discovers that hes a bit of a sellsword. A look through his client list and he discovers that his most recent hires are from JujuTech, and quickly assumes that gojos the one hiring nanami to sabotage him. He isnt exactly wrong, but he isnt exactly right either. Hes only hired to keep watch. Doesnt say that he cant meddle though.

Geto then gets it into his head to use nanamis for hire status against gojo, and hires him to work for him instead—saying that he's gonna pay him double whatever gojo pays him. Nanami accepts. Hes quite literally being paid to betray gojo, doesnt mean he cant betray them back for free though. Geto, quite literally, put a fox in a chicken pen.

Yes, he still does as Geto wishes—targeting JujuTech students and trying to kill them (his attempts are so half hearted though that he just ends up decommissioning them for a bit), targeting and attacking clans (this, hes perfectly okay with not holding back—helps both geto, him and gojo anyways if a few more of these fuckers died), and locating and not killing strong curses (dont mean that he cant leak their existence to Gojo though). Nanamis running the riskiest double con here because hes now officially working for geto, but still helping out gojo LMAO

gojo takes one look at him; blues flash with surprise and reproach. "shoko," he orders, no room for argument. "she's busy," nanami quickly retorts. "she's taking care of the assistants in the infirmary, remember?" "they can wait," gojo says, like it's the answer to the world's most obvious riddle. "i can take care of myself. besides, they're in much worse shape than i am." the senior's eyes narrow, clearly unused to rebuttals on his authority. he cuts the distance between himself and the younger student, face twisting in a disapproving scowl at the sight before him. "what a mess," he clicks his tongue, pointing at the cut, "you're not going to be able to fix that with closure strips. it's too deep. you got thread?" "yes, but," and he watches gojo pick at his supplies, snapping the lidocaine ampule open and filling up a syringe with anesthetic. it happens so quickly, nanami can hardly keep up. he wants to scold the older boy for not putting on gloves, and gojo seems to read his mind, because he grins and dangles the syringe between his thumb and forefinger. "don't worry, i'm sterile." the blond scoffs. "do you even know what you're doing, gojo-san?" "you think i'd wing it?" gojo asks, grabbing the boy's arm and inspecting the gash near his elbow. it's clean, already washed with saline solution, and when gojo carefully spreads the edges of the wound, he can see exactly just how deep it goes. "i may wing a lot of things, but i would not wing fixing up my dear kouhai, nanami-kun. you think too lowly of me." it's as sincere sounding as just about every other word that comes out of the special grade's mouth, which is to say, not a lot. "yeah, well, i can take care of it," nanami insists. "i was doing just fine." gojo rolls his eyes. "nanami-kun, don't be stupid, you can't stitch this up on your own. if you don't want to have shoko patching you up all the time then you just have to get better, alright? the less weak you are, the fewer injuries you get - simple as that." the concise, casual put down makes him glower, but gojo isn't saying anything he doesn't already know, nothing he doesn't already think about himself, so he sighs and extends over his arm to the older boy, who raises his eyebrow. "get on with it, then, gojo-san," he says. and, as an afterthought: "please." it takes gojo a second, as though he wasn't expecting nanami to acquiesce so quickly, but he nods and uncaps the syringe. after applying the local anesthetic, he tears open the suture package, takes it in the needle driver and begins to effortlessly stitch shut the wound. while he didn't think gojo was actually going to wing it, it's still impressive handiwork. it also hurts minimally; nanami can only feel the vague pressure of the needle piercing into his skin every time gojo closes up each stitch. the older boy looks perfectly focused on the task at hand, too; his eyes honed in on the gash disappearing before him.

And some of my nanago interpretation of it!!