I've been sitting on this post for a while, partly because it's taken me forever to type this up and dig all the receipts out of the manga, but I'm done now so okay, here goes.
So. Death Note Light/Ryuk is a niche ship to begin with, but of what content there is for them, I've seen (comparatively) plenty of stories where Ryuk is the dominant one and Light is his plaything and/or victim either willingly or not. Which is fine, but, hear me out: what about the other way around?
What? Well, stay with me here. [LONG headcanon/meta post and manga canon receipts under cut, image heavy, includes references to BDSM.]
Based on the scenes in the shinigami realm where various people are talking about Ryuk's shenanigans in the human world, it seems like most shinigami automatically presume the human to be the dominant partner in a Death Note bond. There's derisive comments about Ryuk having no pride, a degree of shock and disgust at his perceived misfortune, joking remarks about whether he'd make a cute pet, etc. None of the other shinigami even suggest that he's going to be the one with the upper hand; and in fact we know that this is a pretty accurate assessment of how it can work out if a shinigami loses their Death Note to a human and doesn't have a backup of their own, because we see what happens to Sidoh when Mero and the mafia have his notebook. He's well and truly stuck, and ends up pressed into service by them because they can literally hold his life and death over his head. He can't do anything to take the notebook back by force because the rules don't give him enough leeway, and he isn't smart enough to realise he has other options (until Ryuk points it out). That's clearly not a great place to be, certainly if you're unlucky enough to get caught by a human who's brave enough to try and exploit you; so, sure, I can understand why the other shinigami view the "dropped your Death Note" scenario as a risky and humiliating turn of events for the shinigami in question.
Now hold in mind, if you will, that a significant category of BDSM and kink scenarios can be summarised as "choosing for fun and pleasure to get into controllable versions of situations you really wouldn't want to be in without a safety net"; consider the implications of a backup Death Note in a shinigami's hands as the functional equivalent of a very forceful safeword... aaaand now suppose we entertain the possibility that what's really driving Ryuk is not just a desire for entertainment but hidden underneath it, a raging submission/subjugation kink. He dropped the notebook hoping to get that itch scratched, and he sticks around as eagerly as he does because Light's brilliance, arrogance, fearlessness, and casual use and smack-talking of him are doing it for him like crazy.
Like, consider: a Ryuk who on the night following the busjacking incident had to hide under his wings and process his feelings once Light was asleep because it Did Things to him to learn that Light had flat-out used him in that plan without even asking or warning him first. A Ryuk who's letting his apple addiction kick his ass completely on purpose because it gives him a nice low-key excuse to put himself at Light's mercy and have something to beg for. A Ryuk who absolutely would get embarrassingly turned on at being called Light's pet to his face and would flat-out give way at the knees if Light ran with it and threatened to put a collar on him even in jest. Etc.
The real tragedy of this scenario is honestly that Light's comphet-riddled and vanilla little brain would never actually clock what was going on, and consequently he'd never get half the use out of Ryuk that Ryuk would gladly allow if Light knew to lean on him harder. Nonetheless, Ryuk is having the time of his life anyway because he got absurdly lucky: of all the humans in the world, he managed to pick up soft-shinigami-dom Light Yagami, who indulges him with regular treats and playtime and attention (videogame hangout time is canon, remember), allows him on the metaphorical (and literal) furniture without even telling him to take his boots off, rarely if ever asks him to pull his weight but clearly likes having him around regardless, is doing so many fun and clever and horrible things that at times Ryuk can barely keep up with all the entertainment he's getting, and - most delicious of all - has no fear of him whatsoever. Light, by pretty much pure luck, is right in the sweet spot of being instinctively dominant enough to sate Ryuk's kink needs at least somewhat, but tolerant enough of Ryuk's everything to spoil him and let him get away with all sorts of shit; which is a whole additional kind of fun in its own right.
So, that's the constructed narrative for this version of their ship dynamic; but, for real, I think you can pretty much stand this interpretation straight on the manga canon if you're willing to squint even a little. A selection of receipts below:
Initial context. Apparently at least one other shinigami thinks that being stuck with a human holding your Death Note is such bad news that "not even Ryuk" would want that - which is interesting in that it implies he's got a reputation for doing ill-advised, risky or maybe just depraved things already, but the others think that dropping a Death Note on purpose should be beyond the pale for even him.
And literally while that's being said about him, in the very next panel, where is Ryuk? Eating an apple, flopping on Light's bed, and gazing at Light. So smitten, poor shinigami, just look at him. Third chapter of the manga and he's already toast (but he's also, importantly, comfy and well fed...)
Aaaand you don't exactly look like you mind.
Just got manoeuvred into being shot at, having deliberately chosen not to check what the plan was beforehand, and apparently not even mad because he's too busy being thrilled by how clever Light was to put that together.
Ryuk don't just agree with him when he says things like that, people will think you've got a humiliation kink or something.
Openly admitting that Light's companionship is even more of a priority for him than his literal drug of choice... and surprisingly excited about being given a task to do.
Worn out from assiduously following orders while Light wasn't even supervising him, and, as with the busjacking scene, seeming remarkably chill about having been made use of.
Good grief does this even need annotation? Practically on his knees in public and literally eating out of Light's hand. Let it be remembered that Ryuk didn't have to embrace his addiction to human-world apples; he was presumably clean at the start of the series and could've just stayed off them, given that he clearly knows what can happen to him if he doesn't. He 100% brought this one on himself.
More shinigami-realm commentary on the situation, to confirm how this all looks to those who should know. Apparently the assessment upstairs is definitely that Ryuk is the one who should be embarrassed here, though Light's judgement is being called into question as well. (I dunno though honestly, personally I think Ryuk has managed to be really quite cute at several points so far...)
"I just think you should tell me what you'll let me do. Even when there isn't a rule about it." (Okay, this one's so blatant even Light was visibly surprised. Ryuk were you horny that day or something?)
And then a couple more data points from after the timeskip:
A rare moment when Light goes full dominance mode on Ryuk and is flat-out giving him an order rather than appealing to Ryuk's desires for fun and apples, as he more usually does when he wants Ryuk's cooperation. Importantly, recall that at this point in the plot they don't even have a direct bond. Misa is the owner of the only notebook Ryuk is currently bound to, while Light is using Rem's old one which has no attached shinigami. Light has no possible grounds of authority to tell Ryuk to do anything - and yet, zero pushback from Ryuk, who instead goes all-in on the entire sequence of plans that follows this scene even though he's straying well outside his declared neutral status by doing so.
Light questioning Ryuk in front of the rest of the taskforce. Given the actual dynamic between them, and the fact that Light put Ryuk up in the first place to pretending they're enemies(ish) for this plan? This is verging on "playing at interrogation kink in front of an unwitting audience" levels of shenanigans. And yup, Ryuk's still gleefully on board.
A moment that's relevant for showing us the negative space, so to speak. Evidence that Ryuk can and will push back against humans who overstep his boundaries, certainly if he isn't bonded to them - but it seems that Light is allowed to get away with far more than Matsuda. (And also, when provoked, Ryuk apparently looks a bit more like he's on Light's side than he might mean to...)
And finally, this is such a perfectly unfortunate moment of clarity. I love this panel so much. Yes, Ryuk, you are indeed getting used, and if you really didn't like it you could've bailed out years ago. I see you. <3
(I'm sure there's more, I probably missed a few moments, but. You get the idea.)