The door swung open. Lily bounced in wearing the same oversized t-shirt, a small towel draped over her arm, eyes sparkling.
"L-Lily?! What are you doing here?" I yelped, clutching my towel tighter.
"Mom told me to take a bath too!" She tilted her head, completely unfazed.
"Then I remembered big bro was bathing, so I thought we could do it together like old times!" Her big, innocent eyes stared straight into mine, full of pure excitement.
I opened my mouth to say no… but nothing came out. How could I refuse that smile?
She took my silence as permission and clicked the door shut.
"L-Lily…" My voice cracked.
She didn't even glance back. In one quick motion the oversized t-shirt was over her head and on the floor. No underwear, nothing. Just smooth, pale skin and those soft, heavy mounds that looked even bigger without clothes.
Pink nipples already perked up from the steamy air. She kicked the shirt aside and walked straight toward me, hips swaying like she didn't have a care in the world.
"Big bro, can I rub your back?" She was already grabbing the shower puff and peach body wash.
I was sitting on the wide edge of the tub, towel knotted low, water running hot behind me.
"Um… okay… as you wish," I muttered, not trusting myself to say more.
Lily's face lit up like I'd just promised her the world. She stepped behind me, poured a huge globs of soap into the puff, and started slow, firm circles across my shoulders.
"Big bro got so many muscles now…" She whispered happily, pressing her whole body closer. Her soft chest squished against my back, nipples dragging little wet trails every time she moved. The heat of her skin, the slippery soap, the peach scent, everything was making my head spin.
I stared at the wall tiles and tried to breathe normally. Failed completely.
She hummed a little tune while she scrubbed lower and lower, until the puff was teasing the top of the towel. My thing was already half-hard just from her voice and the second she touched me it went full steel.
"Turn around a little, please?" she asked sweetly.
I obeyed like a robot. Now she was kneeling between my knees, water cascading over both of us. Droplets raced down her collarbones, over those perfect round breasts, dripping off her nipples like tiny waterfalls. She looked up at me with those huge innocent eyes and smiled.
"Your turn to wash Lily!" She pushed the puff into my shaking hands. I poured soap with fingers that wouldn't stop trembling. Starting at her shoulders, I tried to be careful, clinical. But her skin was impossibly soft, like warm silk under the foam. Every circle made her chest jiggle. I kept my eyes on her face, but they kept sliding down on their own.
Lily giggled. "It tickles~"
She leaned forward so I could reach her back. That pressed her bare breasts straight against my chest. The soaked towel was the only barrier left between us, and it was doing absolutely nothing anymore.
My thing throbbed so hard the towel tented like a flagpole, poking her her back. Lily noticed in half a second.
"Big bro… something poking me" she whispered, sitting back straight.
I couldn't say anything
"Why is this... Getting big?"
My face burned. "It's… it's just a guy thing..."
"I think I know!" she said suddenly, eyes sparkling like she'd solved a mystery.
"My friends said boys get stiff like this when they really really like a girl. So… big bro likes Lily that much?"She poked the towel right on the tip. I hissed and jerked.
"Yeah" I didn't know what to say to this innocent little angel that it's because of her body and I'm a pervert who is getting hard on because of his sister.
"... and they said it hurts if it stays like this too long…" Her voice dropped to a worried whisper. "Does it hurt right now, big bro?"
It did. Badly.
"Then Lily will make it stop hurting! I don't want big bro in pain." She bit her lip, thinking hard, then gave me the sweetest, most dangerous smile.
I tugged the knot with my fingers. The towel fell away. My thing sprang up, flushed dark, a bead of clear liquid already dripping from the tip.
Lily's eyes went perfectly round. "Waa… it's even bigger than I thought…"
"Lily! You want to help big bro right? Can you hold it with your hands" Something filthy woke inside me as I said it while I patting her head.
"Like this…?" Both her small hands wrapped around it like she was holding something precious. Warm, soapy palms, slippery, perfect. She gave one slow, curious stroke from base to tip.
"Y-yeah… but softer at the top…" I groaned, hips bucking on instinct.
She listened so well. Fingers loosened, gliding gently but clumsy over the sensitive head, spreading the slick liquid in tiny circles. Every time her thumb brushed the underside I saw stars.
"Is this better?" she asked, cheeks pink from steam and excitement.
"Perfect… just like that…" She beamed and kept going, slow and steady, twisting her wrists the way I showed her.
Water poured over us, making everything slippery and warm. Her breasts bounced lightly with every pump, nipples grazing my thighs.
I couldn't stop the little sounds escaping my throat.
"Big bro's thing is jumping so much… it's really cute," she giggled, leaning closer.
"Look, it's crying more…" She scooped the clear drop with one finger, stared at it, then rubbed it over the head like lotion. The feeling made me thrust into her hands.
"L-Lily… I'm close…" She didn't know exactly what that meant, but she felt the urgency. Both hands worked together now, one pumping the shaft, the other gently rolling the head in little circles.
I groaned loud, hips jerking hard. Thick ropes shot out one after another, painting her hands, her face and splashing across her chest. She flinched back by the sudden spurt of white stuff.
"Wow… so much white stuff… it's warm…" Lily looked at the mess on her skin with pure wonder.
She brought her fingers to her lips, hesitated, then licked just a tiny bit. Nose scrunched. "Kind of salty…"
Then she smiled the brightest, happiest smile and threw her arms around my neck, pressing her sticky chest against mine.
"Thank you for letting Lily help, big bro! I love you the most in the whole world!"
Water kept pouring over us. I held her close, heart pounding so hard I thought it would burst.
Guilt crashed in waves, but the pleasure was still buzzing under my skin. I had just let my little sister… no, I had guided her… I had taught her exactly how to…
I was the worst.
Feeling her warm, slippery body pressed tight against mine, those huge, soft mounds flattening against my chest, made my thing twitch and harden all over again.
"Big bro… it's getting hard again…" Lily pulled back just a little, looking down between us with big, confused eyes. She could feel it throbbing right against her tummy, hot and insistent.
To be continued...