Hikaru lives with her younger sister and brother-in-law. She originally planned to move out after the wedding so she would not intrude, but the couple asked her to stay, and the three have lived happily together. One night, exhausted from days of overtime, Hikaru falls asleep almost immediately on the last train home. She wakes in a panic to find her skirt ridden up and her adult brother-in-law staring underneath while stroking his erect cock. Realizing exactly how aroused he is, she begins to tempt him.