The first of the senshi to come into their power -- and the main characters for the first couple of books -- were the inner senshi.
A talking cat named Luna presented herself to a young girl named Usagi, and informed her that she was actually the fighter for justice, Sailormoon. Her goal: to gather her allies and fight her enemies. One of those allies was Sailormercury, who turned out to be a studious girl who went to school with Usagi. They helped out a priestess at the local Shinto temple, who eventually became Sailormars. A little later, a transfer student joined Usagi's school; she didn't quite fit in, so Usagi became friends with her. This girl was actually Sailorjupiter. It took the four of them a while to get the hang of things, but they soon became a potent fighting force, defeating all enemies. Sailorvenus was actually fighting alone for a while under the name Sailor V; when she joined the others, she awakened them to their true past.