Going to pick up his sister from the countryside to the city to travel, Kata's brother was surprised when his sister brought along a very pretty and adorable girlfriend named Ami. On the way back, the young man kept sneaking glances at Ami... with a face clearly showing sexual desire. The three of them returned home and quickly chatted closely while eating. Kata paid special attention to Ami's "every move", even when she was... bathing. That night, because a close friend living nearby invited him over to visit, the younger brother asked his older brother to go out and didn't return until nearly the next morning. Although she doesn't like her sister going out late, today is an exception. This is a unique opportunity for Kata to "kill" Ami. The older brother quickly agreed to let his sister go out with the familiar saying: "remember to protect yourself". And that night, the young man began to act....