It was Raph's fault, really.

Who in their right mind took two showers a day?
That was the first thing that struck him as weird. Then came the late night showers, the go ahead, I'll take mine later. And Raph was always so careful to hide the small bluetooth speaker Donnie had made him for his birthday last year.
Really, Mikey had no reason not to sneak into the showers that night.

Mikey tiptoed around the lair after having waited for Raph to silently make his way into the communal bathroom. Mikey made sure no one was awake to see him press the side of his head against the closed door. He could vaguely hear the sound of running water from the showers.
After looking around to double check no one had seen him leaving his room, he slowly opened the door to the bathroom, then slipped inside.
He automatically went into a crouch. He couldn't see Raph yet but Mikey could faintly hear music playing over the sound of running water. He had been right, Mikey thought with a smirk. When it was Raph's turn to choose the music during road trips or parties, it was always classic hard rock songs or whatever Casey was currently listening to.
But this, it didn't sound anything like it. It sounded like 80's power ballads and Mikey could sense a prank from a mile away.
He drew closer to the showers like a cat stalking his prey. He made his way past the row of lockers that hid the entrance to the shower area, on the far right corner of the room. As he rounded the corner, he pressed his back against the wall and counted to three before popping his head inside.

 
Mikey was immediately assaulted by the moist heat of the room. The first thing he noticed was that Heart was blaring on the tiny speaker, the sound of All I Wanna Do Is Make Love To You filling the room. The second thing he noticed was that Raphael was actually dancing and humming.
This was the best day of his life. Mikey couldn't have been happier even if Santa had come crashing down into the lair to announce Christmas now came twice a year.
The grin on Mikey's face was starting to hurt. He should have brought his phone, this was even better than what he had imagined. Raph never hummed and he never listened to mushy love songs as he dubbed it. Yet here he was, swaying his hips while rubbing soap on his biceps, mouthing the lyrics. His eyes were closed but he had an intense expression on his face, clearly lost in the music.
Mikey couldn't tear his eyes away from his brother, thinking of ways he could embarrass him tomorrow at the breakfast table.
He was snapped out of his reverie by a particular sway of Raph's hips. Who knew his brick wall of a brother could move like that?
With renewed interest, Mikey grabbed the side of the wall he was hiding behind. He didn't dare breathe too hard but the heat and moisture was making his breath more laboured than it should have been. He could feel the skin on his neck prickle and flush. Raph hadn't notice him, and Mikey didn't want to lose a second of the show. To have more material to embarrass Raph, he told himself.

The refrain was coming up, and at this point, Raph's hips were undulating forward and back, the movement making its way to his chest while his soapy hands were busy rubbing small circles around his neck. Each sway was more confident than the last, they started with a snap of his hips and melted into a gentle wave, leading the rest of his body into a sensual dance.
It was hypnotizing to watch. Mikey was supposed to be the party turtle, the one with all the moves but the way Raph was moving his body left his mouth strangely dry and his eyes wide open.
Raph pumped more liquid soap in his hands, never missing a beat, and bent down to rub his legs from his thighs to his calves, one leg at a time. His back was mostly to Mikey, who was greeted with an unobstructed view of Raph's backside and tail.
Mikey gawked at the the short appendage. Raphael generally kept it hidden at all times. He could only get a glance of it when he riled his brother up enough, but then it was all tense and only visible for a short moment before Raph could catch him. It wasn't relaxed and swaying like now. It was like the stubby tail was beckoning him to come closer andand do something.

Mikey shook his head to clear his foggy mind, the heat from the shower was getting to him in weird ways.
It looked like the song was coming to an end. Raph's movement were more sluggish and he was done with the soap. He tapped his foot to the beat of the drums and his shoulders were lightly moving to the fading music. He ran his hands over the top of his head, tilting it back to let the hot water wash away the suds. He was back to humming but his face wore a more relaxed expression with his eyes closed and his mouth slightly open.
Mikey was watching the water run across his face, his lips, his plastron.
He managed to tear his gaze away before the droplets disappeared between the crease of Raph's strong legs. He stumbled for a moment when he snapped his head back too quickly.
He pressed his hand to his chest, feeling his heart hammering behind his plastron. His head was a jumble of half processed thoughts and images of Raph's hips. Sweat was collecting on his brow as he made his way back to the door. As silently as he made his way inside, Mikey got out, careful not to slam the door with his trembling fingers.
He took a few precious seconds to lean against the door and take deep breaths in an effort to push down the excess energy that had built up in his body without him noticing.
He only moved away from the door when he couldn't hear the sound of the shower anymore.

Mikey wasn't sure what to do with the information he had stumbled upon, about Raph or about himself. His prank could wait for now.
Next time he'll make sure to bring his phone to record the whole thing, Mikey thought as he climbed up the stairs to his room.
For pranking purposes, of course.
