As the title says, this is a story taking place in the same world as My lovely older sisters, in which Touma is the younger brother of Oriana and Kaori.
This will be shorter on chapters. Similar to How I married two women in the one k per chapter mark.
Touma was a growing man living with his stunningly hot, beautiful and seductive sisters Oriana and Kaori. Unlike mangas where the main protagonist is incapable of expressing their feelings to their love interest or interests and the love interests, in turn, misinterpret what the main protagonist means if they ever confess, these three siblings didn't have that problem. They were helplessly, unbearably in love.
Oriana and Kaori were fully aware they gave Touma a boner. The two girls sat on either side of him. Kaori in a purple shirt and black boyshorts. Oriana in a white shirt and pink panties. Their bare legs him an eyeful of how sexy they were. They didn't wear bras and their shirts were tight on their chest area, and so he was made aware of their hardened nipple.
Kaori was an Asian beauty, Oriana a Caucasian one. Kaori's long black hair was tied into a ponytail and dangled behind the sofa. Oriana's blonde hair spread around her shoulders and behind her back, pressing against the backrest of the sofa. Touma was pressed between them, their legs constantly rubbing against his own. He was clad in blue shorts and a gray shirt. He ran his fingers over his head, folding his spiky hair under his palm. He sported a boner, and the bulge caught his sisters' eyes more than once.
They held black controllers, Kaori's sporting violet glowing lines, Oriana's the buttons glowing yellow. They played a racing game on wall-mounted flat screen tv. Sometimes when they got into it Oriana would tilt her body with the controller, curving the virtual car sideways. Kaori would almost jump with the immersion and twitch her legs as she played the game.
They both knew, of course, how their bodies rubbed against Touma. Oriana did it again, overtaking another car and suddenly tilting on Touma, pressing the side of her breast on his shoulder. When he was about to tell her to take it off, his words stopped in his throat. Her blue eyes were beautiful, but it was the intense heat in her smoldering look that made him pause. Kaori squeezed his knee, and he turned to her. She was doing the same, giving him the same gaze and rubbing her thigh against his leg. With a wry grin, she asked, "What's up?"
"N-nothing." Touma cursed in his head. Why did he stammer?
"Well, let me let you in a secret." She leaned towards him and sensually brushed her lips on his cheek. She nibbled on his earlobe and whispered, "It's Oriana's eros day."
"What?" Touma asked. Oriana beside him stilled.
Oriana's eros day referred to days where she would be subservient to her siblings. She used a type of magic to locate her targets using trinkets, sacrifices, and offerings to pictures of gods in her room. She was a novice in this type of magic and it backfired horribly the first time she did it. She hated chores but for an entire day helped Kaori clean the dishes and wash the laundry. To cover it up Oriana pretended to start enjoying doing chores even if it was the complete opposite.
At least until that fateful day Touma asked her in jest to give him a blowjob. He was in the bathroom combing his hair. She was on the open entryway with the reflection of her back visible on the mirror above the sink. She stopped walking away, and he wondered if she was going to tell him something else. To his surprise Oriana gave a bashful grin, the blush making her already beautiful face all the more attractive. She pushed him down to sit on the toilet, pulled down his shorts, pushed her blonde hair behind her ear, and pressed her lips on his cock. With a glance up as her tongue probed his head, Touma felt bliss. It was later when his semen dripped down her chin and into the toilet bowl that he wondered if they were taking the next step in their relationship. So he was confused why Oriana immediately ran to her room afterward. He then noticed every odd day when she would try to wear something to cover her ears or act in a manner that was out of place. He eventually learned of her power and its flaws and took her virginity.
In the present, Touma's hand caught Oriana's thigh and he squeezed, drawing a sigh from his beautiful sister. "Is it true?" he inquired. "Answer the question."
"Yes," she hissed as he trailed a finger pressed on her skin up her thigh. "It's one of those days."
Kaori grinned like a pervert. She desired Oriana just as much as she did Touma. To the point he once opened a bathroom and found the two glistening with sweat, naked and fucking, Oriana on Kaori's lap, Kaori's strong and slender arms wrapped around Oriana's abdomen, her breasts pressing against Oriana's back, her face pressed on Oriana's spine, and her lips and tongue rubbing and slobbering spittle on Oriana's skin. A double headed dildo was lodged into their pussies dripping with their juices falling into the water of the toilet bowl. Oriana's hands clutched Kaori's wrist and forearm, and her flustered face was stuck moaning and gasping as Kaori fucked her senselessly. If she was trying to push Kaori's hands or scratch her skin, it was failing. Kaori had super strength and enhanced durability, with the eros day simply making things easier when she took Oriana. Kaori pinched Oriana's nipple and twisted, bit her back and growled. Her hungry eyes made Touma took a step back. He later learned she had a mood swing regarding her siblings, her sexual frustration pent up and contained in a box deep in her heart that eventually explodes and leading to her virtually raping her siblings.
He learned quite well.
Most of the time the three pretend the sexual adventures never happen.
But when they're about to...
Touma smiled mischievously. Behind him, Kaori eyed Oriana like a piece of meat with a flavor to be savored and chunks chewed and enjoyed. He asked her to give him the controller. She did so. He told her to sit between him and Kaori, moving to the side. She did so. He gave back the controller and told her to play the game. She did so. Now and then Touma and Oriana would caress her legs and abdomen, hiking up her shirt until it revealed the underside of her breasts. All the while Oriana would try to push their hands away to no avail. They didn't order her not to resist, but they didn't retract the order to sit between them and leaving her stuck. Touma cupped the underside of her large breast. Kaori pinched her nipple through her shirt. She pulled a purple dildo from her back on the floor beside the sofa. Touma pulled down his shorts and pushed Oriana's panties to the side as he moved behind her. He thrust inside her, drawing a gasp, and Kaori took the opportunity to push the dildo into Oriana's mouth and lubricate the sex toy with her spittle. Touma kissed Oriana's head, taking in the lemonade scent of her hair, and eyed Kaori hungrily. She did the same. Oriana gagged as the dildo reached her throat. Kaori pulled it out with a trail of spittle. She licked the dildo and watched Touma pull Oriana's shirt up to her neck and cup a breast in his hand. Kaori squeezed the other and leaned into her chest, sucking Oriana's breast. Touma was blessed the wonderful view of Kaori straddling Oriana's thigh and suckling her breast, coating it in saliva. Her tongue flicked Oriana's nipple and her teeth bit the areola as she returned Touma's gaze. She pinched the other nub between Touma's thumb and forefinger. Oriana came. Touma followed. Kaori pushed her boyshorts down her thighs, inserted the lubricated part of the dildo into her pussy, aggressively pulled Oriana's hips off Touma's lap and cock, leaving a line of his semen falling into his leg, and dragged her into her arms and knees on the cushion. With a grunt she thrusted the dildo into her sister's pussy, pushing Touma's semen out of Oriana. The girl on girl action gave him a hard on, and he petted Oriana's head and pressed her into his cock, where she took it in her lips and gave him a blowjob like she did the first time, while Kaori took her from behind.