"Sailor Moon SuperS Plus - Ami's First Love" is a 40-minute special that serves as a side story to the "Sailor Moon SuperS" season. The narrative centers on Ami Mizuno, also known as Sailor Mercury, and explores a more personal and emotional side of her character. The story begins with Ami receiving a letter from a mysterious admirer named Mercurius, who claims to have met her at a summer camp years ago. Intrigued and flustered, Ami decides to meet him at a planetarium, where he works as an astronomer.

As Ami delves deeper into her memories, she recalls a brief encounter with a boy named Mercurius during her childhood. The two shared a connection over their mutual love for astronomy and stargazing. However, their time together was cut short when Mercurius had to leave abruptly, leaving Ami with a lingering sense of nostalgia. The special explores Ami's internal conflict as she grapples with her feelings of first love and the uncertainty of whether Mercurius is the same person she remembers.

The plot takes a dramatic turn when it is revealed that Mercurius is being manipulated by the Dead Moon Circus, a recurring antagonistic force in the "SuperS" season. The circus seeks to exploit Ami's emotions to weaken her and the other Sailor Guardians. As the situation escalates, Ami must confront her feelings and the reality of Mercurius's true intentions. With the support of her friends, Usagi Tsukino (Sailor Moon), Rei Hino (Sailor Mars), Makoto Kino (Sailor Jupiter), and Minako Aino (Sailor Venus), Ami ultimately overcomes the Dead Moon Circus's influence and reaffirms her commitment to her duties as a Sailor Guardian.

The special provides a deeper look into Ami's character, highlighting her intelligence, sensitivity, and vulnerability. It also reinforces the themes of friendship and resilience that are central to the "Sailor Moon" series. The narrative balances emotional moments with action, as the Sailor Guardians work together to protect their world from the Dead Moon Circus's schemes.