i'm always a huge sucker for childhood friends aus because that's one of my favorite narrative tropes (childhood best friends to lovers) but with sanuso it makes me feel so insane. i already headcanon that usopp and sanji wish they could've been in each others' lives as children, that maybe if they had each other then things could've been different. the loneliness and isolation wouldn't have hurt so much. that maybe if they had been childhood friends, it would explain the ache they feel whenever they're apart from one another.

when they dock on an island and are on grocery shopping duty together, sometimes the villagers selling them supplies are taken aback by how comfortable they are with each other, bantering, bickering and chatting in their typical dynamic. someone watching them comments that they must have grown up together with how close they are, and while usopp is laughing it off and plays along, it weighs kind of heavy in sanji's mind.

like, yeah, why does he feel so comfortable around usopp, even though he hasn't even known him for that long? which then leads to more thoughts, more daydreaming about scenarios where he's far away from germa. zeff's settled them on a small island where he sets up a restaurant. he meets another little boy who loves playing pirate, always has a fun story to share, lashes so long they remind him of dandelion fluff. he's never once made fun of sanji for being a clumsy crybaby. always shares his snack with sanji despite not having much.

it then happens one night, sanji's quiet but honest confession while they're alone together, laying on the deck of the sunny taking in the constellations. it's not been long since usopp reunited with them after water 7, so the pain is still there, that sanji could've lost him in such a way. that despite their closeness, his own protectiveness of their sniper, sanji couldn't save usopp from his own worst enemy: himself.

"i wish we could've been friends as kids," sanji says abruptly, his face getting hot when he can't help but just blurt it out what he's thinking, especially when he notices something sad pass over usopp's features. he suddenly thinks of usopp alone in his childhood home, nobody to cook him a meal or bandage his scraped knees. usopp then swallows around something difficult, unable to articulate a response but he nods in agreement. he sits up, scrubbing at his face with his still bandaged arm. sanji sees the wet shine of unshed tears clinging to those remarkably long lashes in the dull lantern light, but doesn't point it out. he just continues sitting with him and silently rubs his back.