Luna is a talking black cat that is responsible for finding the Scouts, and motivating them to fulfill their destinies. She gave Serena her transformation broach, and gave Mercury and Mars their transformation sticks. She eventually finds the Moon princess. Along with the memories of the Scouts' past and her knowledge, she is on a mission to re-assemble the scouts with the aid of a talking white cat ( artemis ) with whom she communicates through the Sailor V videogame in the arcade. She is a main motivational source for the less than motivated Serena.
Artemis is Mina's white cat. Before Sailor Venus joins the rest of the Sailor Scouts, Artemis is the cat that Luna talks to secretly, through the computer at the video arcade. Artemis was Mina's cat, before the existance of the Sailor Scouts. He gave Mina her transformation pen, so that she could fight the world's evils as Sailor V. Believing that the forces of the Negaverse would return to Earth, Artemis was an important guide to help Luna to find the other Sailor Scouts. Artemis is a cool cat with an attitude but eventually ( in the later seasons in Japan ) he and Luna have a child named Diana who comes back from the future ( just like Renie ). She is Renie's guardian cat, like Luna is to Serena.
Darien Tuxedo Mask
Tuxedo Mask is one of the more complicated characters of the series as he is Darien, Tuxedo Mask, Moonlight Knight ( more or less =), and Prince Darien. In general he is an ally of the Sailor Scouts, but he does have his own interests, as he tells Serena that nothing will stop him from gathering the Rainbow Crystals. His trade-mark is a single red rose... thrown in battle. It has been said that it signifies his love for Serena. The Moonlight Knight is Darien's soul trying to save his true love. As Darien he is an independant college guy who lives in an apartment. He dates Raye every so often, and has a rather unpleasant relationship with Serena who he lovingly calls "Meatballhead". This relationship turns completely around when Darien and Serena find out who they really are. As Prince Darien (1000 years ago) he was to marry his true love, Princess Serena. When the Negaverse attacked he tried to save her but the forces were too great and they both died. His soul, along with those of the other scouts was sent to earth to be with his true love.
Rini's real name is actually Serena, but so you don't confuse the two she likes to be called called Rini. In Sailor Moon R (the second season in Japan), Rini goes back into the past to find the Silver Moon Crystal, to try and save Crystal Tokyo and her mother. In Sailor Moon S (the third season in Japan), Rini comes back to begin her training as the Sailor Scout of the future moon. She can be really annoying but deep down she really cares for the scouts, especially Serena.