Sailor Moon SuperS Plus: Ami's First Love(1995)

Bishoujo Senshi Sailor Moon SuperS Gaiden: Ami-chan no Hatsukoi

Quiet bookworm of the Sailor Senshi Ami takes pride in her studies, but a rival naming himself "Mercurius" is suddenly outscoring her on the national exams. Combine this with a sudden love letter and a youma feeding on Ami's stress over the whole situation, and Sailor Mercury finds herself in a huge pinch.

(Source: Anime News Network)