Regardless of how students handle the many academic challenges facing them, they all know that there will come a day when they will leave all the hurdles of scholastic achievement behind and tackle the triumphs and sorrows of true adulthood. One thing that many young people don`t realize is that this often means leaving behind the friends that have been with them through their youth.

[description from animenfo.com]

Note:
There are two different Graduation-OVAs with 2 episodes each.
Although both involve the same characters, this one is more of a drama, while the second ("Graduation: Sailor Victory") is more of a parody.