Sailormercury was discovered by Usagi and Luna during the first wave of Dark Kingdom attacks (Manga Volume 1 Act 2 / TV Episode 8). She was Sailormoon's first companion. With Sailormercury's superior intellect and composure, she proved to be a welcome addition.

Sailormercury is the strategist, always analytic and logical. She is a team player in the truest sense -- it didn't matter that she didn't get credit or recognition... the important thing was that she had been able to contribute what she could. The mere fact that Sailormercury had been one of the first to sacrifice her life for Sailormoon (TV Episode 45) shows us that her courage and love knows no bounds.

Sailormercury keeps a very low profile. Too low. She herself asserts that she is the least powerful (TV Episode 45). How good a senshi is cannot be measured by power alone. Power has to be combined with other factors such as strategy, control, presence of mind, etc.

Superficial as it may seem, I believe that the way Sailormercury looks on TV is a major cause for her seeming lack of popularity. Manga fans are more likely to admire her looks because she is consistently pretty in the manga. At times it would seem as if Sailormercury would have very little to say. It is only because she has volumes of thoughts in her mind.