The older brother in the movie is really lucky to have a sister Tachibana who is not only obedient and gentle but also very understanding of his feelings. Having lost their parents early, he had to spend his entire youth raising his little sister until she grew up, which is why she is very sympathetic to what her brother is going through, especially the repression of his sexual needs. For this reason, whenever he comes home from work stressed and tired, she always expresses her desire to help him relieve that pressure by using her body to provide him with moments of ecstasy and refreshment beside his loved one. She is indeed a lewd sister.