Pretty Guardian Sailor Moon S01 E02 Ami-chan Joins Up

Ami Mizuno is the highest ranked student in Usagi's class, and Usagi manages to befriend her despite their academic differences. But when Luna suspects that Ami might be Senshi as well, Ami also suspects that as the reason for Usagi's friendship and refuses. When she is attacked by a Youma, Ami realizes how true a friend Usagi is and awakens as Sailor Mercury.