Chapter Text
Billy Hargrove and Steve Harrington had basically hated each other on sight. Since Billy moved to Hawkins they had been locked in a battle of wills, circling each other, poking, each trying to prove himself better than the other. 'A ridiculous display of pointless machismo' is what Nancy called it, which Steve could never quite argue with. It's not like he even wants to be King of Hawkins High anymore, but to let Billy take the role just seemed a step too far.
On this particular evening, Billy was pushing at Steve by showing up to his house party, and Steve was pushing back by pretending he didn't exist. He kept an eye on him though, in case he tried anything, but so far Billy had just spent the evening doing keg stands and showing off his abs.
The party was winding down when Steve wandered out to the pool to find Billy smoking on a lounger and staring at the water with something like longing in his eyes.
"Cute garden party, Harrington." He calls, words dripping with disdain. "Bit light on the cucumber sandwiches though."
Steve rolls his eyes and does not dignify this with a response. Instead he kicks off his shoes and sits on the edge of the pool, dangling his feet in the water and sipping on his final beer for the night.
They sit in silence, drinking and smoking and ignoring each other, until Steve decides he's going swimming. He gets up and strips, which causes Billy some mild alarm before he realizes what's going on. Steve dives in, forming a graceful arc through the air despite the alcohol running through him.
"Shit form." Billy remarks as he surfaces, earning himself a glare.
"Think you can do better?" Steve demands and Billy growls but doesn't reply. "What's the matter Hargrove, can't swim?"
"I could outswim you in my sleep, asshole."
"Oh yeah? Prove it then."
Billy hesitates and Steve sneers at him. "What's the matter? Scared you'll ruin your perm?"
Steve splashes some water in his direction and suddenly the night takes a turn for the weird. Billy freezes as the droplets hit across his face and chest. Steve takes a step back, eyes fixed on the spectacle, as his form is obscured by swirling, shining, particles that spiral closer and closer around him. When the air clears, Billy's lower half is no longer clad in tight denim.
"What the fuck?" Steve mutters as he takes in the other boy's changed form. A tail. Billy Hargrove has a tail. It's a green-blue colour, reminiscent of the ocean, and where the low lights from the house hit it the scales sparkle with a shade remarkably similar to his eyes.
Billy seems frozen still and the boys stare at each other in surprise and horror for a moment.
"Shit." Billy is the first to break the silence.
"What the FUCK?" Steve repeats his earlier question.
"Shut up. Throw me your shirt."
Steve blinks at him. "You've never willingly worn a shirt in your fucking life. You grew a TAIL and now you want a SHIRT?"
Billy throws up his hands in exasperation. "I have to dry off to turn back moron."
Steve blinks in surprise but figures this makes as much sense as anything so he heaves himself out of the pool and pads over to his pile of clothes to toss over the shirt. Billy catches it and starts swiping at his chest angrily. Steve watches the other boy as he mops up every drop, and eventually the sparkles return, shortly followed by his legs.
"Want to explain what the hell that was?" Demands Steve as Billy gets up and lights another cigarette.
"Not really." The blonde turns and starts to saunter off while Steve gapes at him.
"Wait, you don't just get to leave after that!"
Steve moves to chase him but Billy whirls round and the look of rage and desperation in his eyes gives Steve pause. Billy just snarls and then takes off again, rounding the house and vanishing before Steve can decide what to do.