@greenpactbosmer Thanks for the ask!

Headcanons... ooh boy, well...

(Oh and I saw you had another ask there too but I think I may have misunderstood the prompt/what was being asked? In any case I should probablt edit the paragraphs of brain vomit that came out of that but until then here's more paragraphs of brain vomit, uh... sorry 😔)

Anyway...

Headcanons for lawryght can vary greatly from fic verse to fic verse but let's see curtent HC generally...

These three getting together in a canon-like universe...

The RyukxLight will either be established relationship or at the very least Ryuk is more helpful to Light and his plans than in canon to the point Light feels secure enough in his position so he can give L a chance and not feel like he has to kill him immediately so a relationship could actually develop between Light and L beyond "oh no, he's hot... I still have to kill him." (Also expect Light to be even more arrogant and insufferable because he thinks he's immortal and has the power of deathgod and anime on his side.)

Ryuk and Light getting together: And then they were roommates (oh my they were roommates) and there was only one bed--Shinigami don't really need to sleep but Light doesn't know that and the bed is comfy so Ryuk doesn't fell the need to tell him.

They are both extremely bored. Ryuk is absolutely fascinated with this human--he may not be on Light's side (or so he claims) but the entertainment value is beyond his wildest dreams. He is smitten, even if he doesn't admit it. If Light is curious about something hell try at least once... Or Light may be trying to get free Shinigami eyes out of him and they catch feelings.

L enters the picture... Ryuk doesn't mind sharing 1. Hes immortal and bored and... two interesting humans! This is so cool! 2. Shinigami don't have the same ideas about monogamy. 3. Headcanons about Ryuk vary depending on if rule 36 valid up to this point in the ficverse. (I.e. Chad!Ryuk vs. Virgin!Ryuk)

L and Ryuk--L is very disturbed to learn that his case actually has a supernatural component and is more leery of Ryuk than of Light at first. This lasts for all of the moment it takes to remember that Light is Kira and Ryuk is afraid of tennis balls.

After 5 minutes of soul searching, L can admit to himself he has a thing for monsters--both internal and external.

Assuming they are all alive and this takes place in early canon this shippable version of L is probably more interested in having fun then bringing Kira to justice. Either that or he has become disillusioned with the status quo or hurt and and wants revenge to the point that he's willing to entertain Light's way of doing things.

If its post series, maybe Ryuk is bored so goes looking for Light in Mu and ends up pulling both Light and L out of Mu because their souls are intertwined and once restored as humans or Shinigami or something shippable in the afterlife then it's just learning to rely on each other as they forge a new arrangement in the Shinigami realm.

Top/bottom it's not assigned seating Regardless of bedroom positions or what arrangement they have out of the bedroom Light is the dom/one in charge of this arrangement in bed... but subs L and Ryuk unionize and gang up on him. Light is a dom in bed but not always a top. L as a sub but not always bottom. Ryuk as a service top or power bottom. Ryuk doesn't really feel pain like humans do and will go with whatever he and his partners find interesting.

Contrary to rumor Light and L aren't always fighting over who gets to top. Fighting is for chess matches, clashes of ideology, and the last chocolate eclaire--not the bedroom. Consent, safe words, and mutual respect are all very important.

(The safe word is vegetables)

Light is very dom. In every relationship before or since. Except there's Ryuk, looming over him. Making him feel kinda excited and confused and then theres that stupid sexy voice of his... But ryuk is the exception. (But he might let L fuck him if he asks nicely and submits to Kira's reign.)

When they sleep together Ryuk likes to keep them both wrapped in his wings. He likes being the little spoon sometimes though...

L gets Ryuk addicted to apple desserts.

Light frequently ends up cleaning up after the other two. Ryuk helps when he remembers but typically L is a brat.

Light: How can you stand to live like this?

Ryuk: I was formed in a dustbowl.

Light: Yes, it shows.

L [throwing candy wrappers on the ground]: Why are you doing that, that's what Watari is for?

Others who might potentially join the polycule under the right set of circumstances: B, Mikami, Aiber, Matsuda...

Some very noncanon AU ideas...

Superhero aus (current wips)

Winning and ruling the world(s) au (current wips)

Light gets in trouble (of either a mundane or supernatural variety) and Ryuk goes to L to ask for his help because he's the only human he can think of who would be clever enough to help Light and because of supernatural restrictions Ryuk can't save Light by himself. L is annoyed to have his fun ruined by having it confirmed that Light is Kira in this way, pissed that Light could get himself into a situation like this, and also pissed at himself that Ryuk doesn't even need to threaten him to want to risk everything to save him. After they save Light, L decides there's no point in continuing the kira case because it no longer interests him. He returns INTERPOLs money and after Light recovers from his ordeal the three go on vacation looking for something interesting but less hazardous than their previous ordeal. L becomes fascinated with the supernatural and wants to go ghost and cryptid hunting, seeking out ancient mysteries and Ryuk has plenty of leads in that. Light is still more interested in becoming god of the new world but "fine, if you guys insist..." (he doesn't want to admit he's having fun too). They drive around in L's pink crepe van huntjng ghosts, solving mysteries. Light occasionally writes the names of murderous jerks and people who are assholes to L thst they meet along the way while Ryuk laughs and L scowls in a mildly disapproving way but never really discourages him.

Au inverting the dynamics so its established relationship of lawlight first and then Ryuk joins the polycule: AU where Light and L are the same age and are childhood friends and when Light finds the Death Note they become Kira together. Ryuk is fascinated by them both and slowburn they realize their feelings for each other.

Or... Human!Ryuk and mundane college AU Ryuk is in a metal band and is probably studying art and helps rival law students Ligtt and L to chill... at least until Ryuk gets in trouble for drug possession and then Light and L compete to be his better defense counsel.

Monster AU werewolf or vampire au that's canon adjacent--Ryuk bites Light, Light goes on to monster better than Ryuk does then Light bites L, the monster hunter who falls for him...

7. Haunted house au

8. The quarantine au--Light is annoyed because now killing as Kira feels rather pointless. L is annoyed because this is boring. Ryuk is having a blast because they're playing with him a whole lot more. If L and Light doesn't just use the L screen, Ryuk is always in the background, having floating, juggling apples photobomb the zoom calls.

And suddenly Ryuk is important.

Ryuk runs errand for them because he has no danger of catching the plague. They play video games, watch movies, bitch at each other, and get into pointless arguments over stupid things.

Also L makes them custom masks modeled after Ryuk's fangs just because.

Other ideas:

Wammys house and lawryght

Option 1: Wammy's house tooth rotting fluff, adopting all the orphans

Option 2: Wammy's house evil, B was right. It's really just about being raised as a weapon. It's like the stormtrooper program for genius orphans that may not have actually been orphans before the institute took an interest in them.

Option 3: Wammy's house complicated. The institute really is trying to do better, is the best place for the kids and while not perfect its closest thing to home/family they have.

Lawryght and Morality

These 3 can be awful enablers of each other's worst qualities. Then again...

Light: Huh, Ryuk thinks we're going too far. Maybe we should rethink this.

L [already has the prisoner tied up and being forced to listen to polka music on repeat]: But where's the fun in that?

Finding a home together

With Kira and a Shinigami as his boyfriend L feels secure enough to do more normal things he's been denied all his life.

With Ryuks help, Light finds the names of all of L's major enemies and gets to writing in the Death Note.

Light: Be mad if you want. I'm not sorry.

L tries to be mad, and fails. He can't help but feel relieved that they're gone.

He might even entertain the thought of having a permanent address.

He still enjoys traveling though.

Also L gets a kitten

The cat loves chasing Ryuk's feathers.

The cat likes Light's lap the best because Light went out of his way not to look at the cat.

....