Luna is Usagi's guardian cat, and therefore has a big responsibility. After all, if you had to chase around an irresponsible, flighty klutz with no grasp of the important role that's been placed on her shoulders, you'd be a bit overwhelmed too. Luna deals with this by nagging Usagi, perhaps a bit more than she should, but only because she cares about Usagi and their mission so much. On a more personal note, Luna is susceptible to crushes--she falls madly in love with a young (and human!) astronomer named Kakeru in the Sailormoon S movie, and later with Yaten Kou (Sailorstarhealer's civilian form) during the Stars season. However, Luna's true love is Artemis, and their child from the future (who returns to our time) is Diana. Artemis is Minako's guardian cat, and therefore was technically the first guardian cat, since he showed up to guide her back when she was Sailor V. Artemis is much more apt to be susceptible to fits of silliness, but that's not necessarily a bad thing; after all, it's been said that Luna would be a little easier to take if she loosened up a little. Artemis is a wise cat, and enjoys a much closer relationship with Minako than any of the other girls are with the cats, even Luna and Usagi; I suppose that's because they've known each other longer. Arty always tries to correct Minako when she botches proverbs to suit her own purpose (for example, eating all the chocolate chips while baking and then claiming it's an example of "You can't zip one's mouth"); otherwise, he has few problems with Venus, since she's a bit more seasoned and responsible than Sailormoon. Artemis has always been in love with Luna; they have a child in the future named Diana, whom he also loves dearly (if you've ever seen the episode of Sailor Stars where Diana and Chibi-Usa are leaving to go back to the future, you'll see just how much--Artemis is sobbing in the most heartrending way). There's not too much to say about Diana; she's just a kitten, after all, and she's not really anyone's guardian. However, she is a good friend of Chibi-Usa, and largely replaces the Luna-P as Chibi-Usa's constant companion when she returns to our time in the SuperS season. (Her choice of transportation is as cute as she is; she likes to ride on Chibi-Usa's head.) Diana's voice is just sooo adorable, and she loves her family and is very polite, referring to the inners as "Makoto-san" et al, and Usagi and Mamoru as "Usagi-sama" and "Mamoru-sama", respectively. (After all, in her own time--the future--Mamoru and Usagi are King and Queen.) She loves to hear stories and learn about life in our time, displaying curiosity typical of human toddlers as well as, apparently, kittens.