Armin's heart had always been with the sea. That was a poetic way of putting it, but it was true enough. He was fascinated by its size, its fathomless depth, all the wild and strange creatures that were rumored to live there.
That last bit was how Eren wound up in a bathtub with his legs wrapped up in a tarp and ropes. Armin wanted to try something new. Armin wanted to roleplay. Armin wanted Eren to pretend to be something called a merman. Armin was at the side of the tub, naked and flushed and very nearly shaking with excitement, and Eren could not help but play along. His hard cock, thankfully spared the tarp, betrayed his interest.
Armin's eyes raked over Eren's bare chest, down his stomach, and over his "tail". His gaze met Eren's, lidded and dark. He took a deep, shivering inhale, and let it out on a long sigh of Eren's name.
"Eren. Tell me about your watery home."
Eren searched his scrambled thoughts, drumming his fingers on the side of the tub nervously. Armin rested his head on his folded arms, his gaze rapt, adoring, and hungry with lust. Shit, Eren had better make this good. He didn't get wrapped up in this tarp to not get laid.
"It's uh…wet. Really wet."
Armin shuddered, his eyes rolling back in his head as his hand drifted down between his thighs. "Oh…I bet it's salty, and so big…"
"Really big," Eren mumbled, driven to distraction once more at the sight. "Real salty. So big you can like…swim and not reach the other side for a while. Probably?"
Armin's mouth fell open, red and wet, as his hand picked up speed. "I'd swim so hard that I'd go under and the salt would get in my mouth, all in my mouth," he whimpered in a rush of words. "What else is there? What other fantastic creatures?"
"Uh, shit, more—" Eren swallowed hard. His own hand seized around his cock, no longer able to bear the lack of attention from Armin's touch. "—more like me, I think, with, with tails, and like—five tails. Maybe more."
Armin choked on a sob. "So many tails, I can feel them splashing water on my face, Eren, please, do it, do it to me now—"
Eren swept his arm under the water in the tub to give Armin a mighty splash. Armin jerked his way through the spray, coming all over himself as Eren showered him with splash after splash, his blond hair sticking to his cheeks and slim, pale neck. After he was spent, there was but a shivering, meager few centimeters of water left in the tub.
Eren shifted awkwardly, his cock still painfully hard. Armin clambored into the tub with effort, flopping onto Eren, and kissed a messy trail from his jaw to his straining erection. Eren groaned and grabbed a fistful of damp locks to anchor himself as Armin swept him away with his practiced lips and tongue.
Maybe next time he could convince Armin to wear the tarp.