Goukaku No Tame No! Yasashii Sankaku Kankei Nyuumon

Middle-schooler Mayuki wants to enter Ohtomo high school to join her beloved senpai Akira. Problem is: her grades are so terrible there's no way she can make it into such a high level school. Thus her mother hires a high school girl named Rin as a private teacher to help her daughter. Seeing how the girl looks so much more mature than her, Mayuki ends up asking Rin to teach her more than just school subjects…