do you think there would have been watari/L shippers within the death note universe?
personally, i think pre-kira, there was a small fandom surrounding the top detectives like L, deneuve, and coil, and most of the people in the community would ship them amongst each other. but there would be a dedicated subsection of the fandom made up of mostly people whose favorite detective was L who were absolutely obsessed with watari/L. i feel like most of the fics would either be really soft fluff portraying them with a sort of king/knight dynamic, or shameless smut of a bdsm dom and his hyperobedient sub.
post-kira, the detective fandom tag on ao3 would get flooded by kira/L fans who are unfamiliar with the fandom's history, inside jokes, etc, thus causing the older fans (especially ones who like deneuve or coil more than L) and the watari/L fans to develop a superiority complex over the new fans since they're, like, veterans or something. i don't know
(teeeeechnically death note takes place at a point in time slightly before modern fandom, the way we know it, but let's pretend haha)
while that kind of fandom would definitely see a lot of new people joining (as is the case with most fandoms when A Big Thing Happens, in this case the lind l. tailor broadcast), the impetus of kira/L would probably still come from the og fans themselves. prior to the broadcast there'd be theorising on if/when L would get involved, i imagine, and a select few fans would already be writing kira/L fic. mostly a crackship thing at that point, you know.
(also there is DEFINITELY already kira rpf, which exists separately from the detectives fandom at the time, so kira/L is crossover created by the fans who are in both communities)
fic of L, deneuve and coil setting their differences aside voluntarily or being forced to team up in various couple or threesome constellations to solve the kira case - and have a lot of very plot relevant gay sex on the side - springs up almost immediately too. sometimes kira kills one of them to heighten the drama. L taking the case, getting killed and then deneuve and coil banding together to avenge him is a fan favourite.
the watari/L crowd are on the ball as well: you've got the obvious where one of them gets killed by kira and the other tearfully avenges them. you've got watari getting kidnapped to blackmail L (which was probably already pretty popular in watari/L fics tbh; it's just good angst). and of course that one writer who has every watari/L shipper scream praise and obscenities at them in the comment section because 50k words into a fic, they drop the reveal that watari was kira all along and L is completely at his mercy now and things get REALLY dark REALLY fast.
and then tailor gets killed live on television and L directly challenges kira. the few fans lucky(?) enough to live in the kanto region who actually saw the broadcast in person come in screaming and crying, first liveblogging what's happening and then posting recordings uploaded to youtube, and the fandom LOSES ITS MIND. it's the middle of the night for some of them, but it does not matter. everyone is blowing up the message boards (or discord channels, or wherever the fandom is congregating), the first few fic writers are already hard at work, fanart is being created, the 'lore' people are drawing extremely funny conclusions about L's personality based on this daring move of his. it's a wild night/day for everyone.
and then... well. the excitement is so intense that others from outside the fandom bubble take notice. probably also a healthy dose of people going "haha what if anyone shipped kira and L together and wrote fic what a hilarious and unlikely idea" and then being shocked when searching the pairing on ao3 - or whatever the in-uniserve equivalent would be - brings up actual results. screenshots get passed around, there's the first inklings of disdain from the uninitiated (isn't it weird to write fic about real people? isn't it kind of fucked up to write fic about real life crimes and murders, especially?), maybe a small news article reporting on the fandom as a curiosity. you know how it goes.
but all the attention doesn't just attract the ones who find it weird or creepy. more than a few people look at the idea of shipping kira/L - or making fan content of kira and/or L in general - and go "i hope this doesn't awaken anything in me" and then (spoiler alert) it definitely awakens something in them. here is where the big influx of new people happens - and while yes, some og fans would definitely be disgruntled by the upset, it's probably just a lot of excitement for the most part, a lot of art and fic and what have you being created because there are suddenly so many more people.
this would of course lead to ship wars (it always does lol) - the kira/L crowd, mostly newcomers, might not even know about deneuve and coil and watari because their only point of reference is the broadcast. cue the og fans creating big 'lore' summary posts with all the important info and fandom history. some of the new fans don't care and will never read them, but i like to think that it wouldn't be a stand-offish 'old vs new' mentality. fandom isn't about animosity, it's about showing the thing you like to other people.
the detectives fandom is pretty old; it has been around at least since L started solving cases, and there was probably a select few people who shipped coil and deneuve and other top detectives even before that. (hilariously, that means there were probably newbies who came into the detectives rpf fandom when L showed up and had to be lectured by those fandom olds back in the 90s or whenever haha)
of course there will always be bad eggs. people who look down on the newbies and go "i liked x before it was cool." you always have people like that, but they're not usually the majority. most fans would just be excited that there's suddenly so much happening in their previously so tiny community.
one thing that might ruffle a few feathers is the way L is portrayed visually. before, it was likely a tma jonathan sims situation where obviously nobody had any idea what L looked like, so there was sort of an agreed upon 'fanon' look for him that artists who drew him and writers who described him in text would reference. after the lind l. tailor broadcast, a lot of the new fans probably start drawing L as looking like tailor just because it's a convenient visual reference (and because tailor is admittedly kind of good looking. which of course brings with it the moral handwringing of whether it isn't kind of fucked up to draw fanart of a guy who got killed live on tv, and who was also a criminal on death row)
(also, consider the tiny subset of the fandom who ship L/tailor and make up AUs where he wasn't actually a criminal at all but L's childhood friend who has helped him solve cases all along and sacrificed himself for the greater good and L is mourning him fiercely. anyway)
then again, back when the fandom was tiny they probably also had their fair share of debate about what L and watari look like (and deneuve and coil, if they were anonymous detectives. otherwise they would get portrayed the way they look irl, obviously). tiny fandom wars were waged over their ages, their backstories, what the exact power dynamic is between them.
top L defenders go to bat for the master/servant dynamic while top watari fans shoot back that L could just as well order watari to top him, or even headcanon that watari is the one in control actually and L is just his mouthpiece. "watari didn't work for L; L worked for watari," as the german death note audio drama would put it (reset the clock, i've mentioned it again). watari gets drawn in the trenchcoat+hat+mask combo A LOT and it's generally agreed upon by watari/L shippers that L finds this outfit extremely hot and has ordered watari to keep it on during sex at least once.
also kira gets drawn as an eldritch horror creature with tentacles sometimes for obvious reasons. the doujinshi are wild.
og fandom in-jokes for your consideration:
personally apologising to L (primarily when posting smut) - the fandom likes to joke that L probably keeps tabs on what's being said about him online, mostly to squash attempts to locate/identify him and other nefarious plots, and is therefore probably at least tangentially aware that there's fanfic/art and stuff being made of him. opinions vary on 1) whether he reads any of it and 2) if he is actually secretly One Of Them
variation of that last point: "i'm not L." which is exactly what L would say if he were one of them, of course. there's one fan in particular who has been jokingly suspected of being L for years because of their really specific headcanons for him
watari's height - nobody has any hope of figuring out what L looks like, but there exist at least a few photos of watari and the fandom has been desperately trying to figure out how tall he is based on the height of the people he's been photographed standing near. general consensus is somewhere in the 5'10 area, but there's one person who stubbornly insists he's 6 feet (it's me. i'm that person)
there's an infamous watari/L crackfic where orgasming is the only way L can solve cases, and all that that entails. it's considered an integral part of their fandom's history and is one of the first things the new post-tailor broadcast fans are subjected to when they join