Flandre sat in the basement of the Scarlet Devil Mansion, isolated as she had been for almost her entire life. The only person she saw since then was the chief maid, a woman named Sakuya. But tonight, someone else would enter Flandre's cell. A stranger walked into Flandre's prison. From the light shining outside, the stranger appeared to have the same light purple hair and pink mob cap that reminded her of her sister, Remilia. The stranger closed the door behind her, once again darkening the room. Flandre had never seen anyone like her. As the stranger approached Flandre and gave a warm embrace, Flandre felt her very form change. Was she some demon? She tried to break from the "demon's" grip, but the "demon" held fast to her.
"Flandre, little sister, don't be afraid." Her voice started out deep and briefly changed to one all too familiar to Flandre.
"Remilia! Sis, let go! What happened to you?" Flandre's voice slowly evolved to become just as deep and masculine as the "demon" standing before her.
"Just relax. This'll feel wonderful." Their clothes dissolved in a bright mist, leaving very different bodies from those that the sisters were used to. Firstly, their chests became more flat. Secondly... Flandre looked down at a protrusion growing from her crotch and pushing against her sister's thigh. This was something new to her.
"Um... Remilia, what's this?" She indicated the long object with her hand.
"Honestly, I have no idea." Remilia kneeled to face Flandre's solid, hard shaft. "But it feels so good to have someone suck on it." She took the tip of the pole into her mouth. Flandre gasped as an intense wave of raw pleasure beyond her imagination began to consume her. She was at a loss for words. An "o" formed from Flandre's mouth while Remilia's tongue swung over the tip of Flandre's shaft. Flandre couldn't move while Remilia tickled every inch of her body by only moving her tongue. Something told her to push Remilia away, but she couldn't respond to that gut feeling that she was going to die. Her groans reached a peak when Remilia forced the whole thing into her mouth.
"aaaaaaahhhhh!" Flandre felt her seven inches being forced down Remilia's throat. Her feet crawled slowly backward trying to force herself out of Remilia's mouth. But Remilia's legs inched forward at the same rate. Eventually, Flandre backed herself into a wall. After some whimpering from Flandre, Remilia stood up and brushed up against Flandre, pressing her pulsing member against Flandre's thigh in doing so.
"nnn... mm..." Flandre steadily pushed Remilia out of the way so she could flick herself along Remilia's thigh. "aah... ahh... ha..." Remilia forced the two back together, each now groping the other's thigh with their pulsing shafts. "aaaaaahhhhh... Remilia..." Flandre began to lose herself to euphoria. She dug her fingers into Remilia's back. "aaahhhh... aa... nnnnng... AAAAAHHHH!"
Flandre released a hot white liquid onto her sister's thigh. Her eyes shot open as her screams continued and abruptly stopped. She released her hold on Remilia and her eyes closed. Remilia kissed her sister and a bright mist reclothed the two. Soon, their feminine bodies were restored. Remilia laid her sister on the floor and turned. When she reached the door, she opened it and left the room. As she closed the door, she gave some parting words.
"Sleep well, little sister."