Yurikko Jogakuin ~Motto Ijimete! Onee-sama~

One day, Kei is saved by a girl when being molested by someone in a crowded train. Who saved Kei is a girl in a school uniform. Kei asks her name, but she doesn't answer, "Just call me sister. See you again." She leaves soon.... "Yes, sister. See you again!" Kei decides to take action to see her again....