Sailor Mercury was the next to join up. In the manga, Mizuno Ami's
name was brought up because she always scored first on tests.
However, in the anime, she transferred in from another school. In the
manga, she received her henshin stick/transformation pen from the
Sailor V video game as a prize for scoring well. At the same time,
Usagi receives her disguise pen. But in the anime, Usagi has already
received her disguise pen before she ever meets up with Ami. And in
addition to that, Ami does not receive her own henshin stick until
after she's attacked by a monster. Then, Luna slides it across the
floor with instructions on how to use it, and Ami quickly becomes
Sailor Mercury and possesses full knowledge of how to use her
powers.