Mizuno Ami / Sailor Mercury

Mizuno Ami is a quiet, shy, intellectual girl who happened to make friends with Tsukino Usagi. Thus, ended the quiet aspect of her life. She is extremely intelligent - it is hinted in one episode that her I.Q. is 300 - and even goes to a second cram school. In the NA version she lives in an apartment, but in the JP version she lives in a mansion. Her mother is a doctor and her father is painter. Her parents are diviorced, and Ami lives with her mother. Ami aspires to be a doctor one day, and was even accepted to a school in Germany to study early. But she decided to do that later when she realized how much the Senshi really needed her.Ami is a kind and loving soul, a bit of an introvert, and always comes up with the best plans - usually better than Usagi's, but that's never very hard. She even has a boyfriend of sorts, who learns who she really is, but that neither scares or bothers him. He merely accepts it as another part of the girl he admires, and keeps her secret like a trusted friend. Ami has a tendency to blush whenever he is mentioned in her presence.
 
 

Ami Mizuno's secret identity happens to be Sailor Mercury. She is the main advisor and strategist of the group, being the only one who can usually think clearly enough to come up with a workable plan.  The others respect and admire Sailor Mercury as more than a friend or teammate, but as a problem solver and a genius as well. Her powers, although seemingly weak, can be vital in a battle. Shabon Spray is a shower of harmless bubbles  that manage to fog up the entire area, thus making it difficult for the enemy to see. Mercury also has an amazingly powerful little computer, one as a visor and one as a handheld device, both helping her find ways out of mazes and enemy weaknesses. If it wasn't for these computer gadgets and Mercury's immense intelligence, the Senshi would have been doomed several times over by the time they had made it past Nephrite, if they had made it past Nephrite at all. Mercury was the first Senshi that Luna discovered after Moon, and the first real comrade Sailor Moon made after Luna. All this definitely makes Sailor Mercury necessary for any Sailor Senshi mission.