Simplify the following text for a Grade 8 native English-speaking person.
Original: Before the Sailor Moon manga appeared , Takeuchi had written Codename : Sailor V , which centered around just one Sailor Senshi .
Simplified: They are named Sailor Mercury , Sailor Venus , Sailor Mars , and Sailor Jupiter . They make up a team called the Sailor Senshi ( Senshi means soldier or guardian ) .