Marshmallow Little Sister Succubus #1

Story

Keisuke Tsukikawa, who has a father who flies around the world as an archaeologist, on the night he loses the necklace his father gave him in childhood, has a dream in which, while sleep-paralyzed, he is attacked by his stepsister Saki dressed as a demon. Feeling guilt over fantasizing about Saki, whom he raised so preciously, even in a dream, Keisuke is found out by his classmate Riri Manabe, who belongs to the school's folklore research club with him, and Riri reveals that she and Saki are truly lust-demons, succubi. Having lost the demon-warding necklace, Keisuke has his body's movements sealed by Riri too, and is squeezed of his semen. Saki, whose magic power had long been sealed by the necklace, becomes her alternate personality Saki and attacks Keisuke again while he is in the bathroom, confessing the feelings for Keisuke that grew within Saki, and grows so absorbed in the act that her magic power runs dry. Before Keisuke, bewildered by his beloved sister's transformation, further trouble erupts... *No bonus footage is included.