My sister Mitsuki, who is uncomfortable talking to people she doesn't know well and feels shy when she's watched, has recently become incredibly proactive when she's cosplaying, as if she's a different person. Today, she's participating in a cosplay photoshoot with her brother and his friends, but the atmosphere gradually becomes lewd. She is forced to wear a penis, has it twisted into her vagina, and while her whole body trembles, she reaches climax.