Recently, 'Saki' has been worried about her brother 'Mamoru,' who seems to be down. After listening to him, Saki learns that Mamoru, who doesn't even understand the meaning of sex, is being bullied at school. When Mamoru asks a question while feeling depressed, Saki advises him, 'Siblings can't do that.' However, after an incident involving Mamoru at school, Saki decides to take off her clothes for the sake of her adorable little brother.
