Prior to Sailor Moon, there was Sailor V.
The Sailor V series only takes up two volumes but was published before Sailor Moon. It relates the story of Sailor V, later known as Sailor Venus, in her first yearish of being a sailor scout and battling dark forces, in this volume the Dark Agency which seeks to drain power from humans.
The first volume is more of an introductory and we got to see how Minako met Artemis and became Sailor V and why there is a Sailor V game. It's monster of the week as the Dark Agency creates new villains to try take over Japan.
It's a fun book, and it's nice to see where the story started, but having already read the next one and the first few volumes of Sailor Moon (I'm rereading them), but it's not as good as the rest.