Chibiusa makes her first appearance in the manga by way of her most favorite entrance: she explodes into the air directly above a tender moment between Usagi and Mamoru and then brains Usagi with her cute little Chibiusa bottom, thus paving the way for her to take up the newly vacated space in his arms and steal a kiss from papa. Usagi is of course not impressed and they go through a similar 'Who are you, I'm Usagi' 'No fair, I was Usagi first' kind of exchange and then Chibiusa pulls a gun on Usagi and having worked out who she is, demands the Ginzuishou. She claims the gun is real, but Usagi doesn't give up the crystal, and when the gun fires Usagi gets only a ping pong ball to the head while brave Mamoru wrestles the gun away from Chibiusa. This tactic having failed, she wriggles away from Mamoru and runs off alone.
The villains in this arc are of course the Black Moon family, and at this early part in the story it is hinted that Chibiusa may perhaps have some connection to Cooan (similar hairstyles and all) but this of course is just a red herring. Of course, given the similarity and the fact that the Black Moon family is after the Ginzuishou as well, it's understandable that the senshi are kind of antsy on trusting a weird, rude little kid. Ah, Chibiusa has yet to display good manners.
After Chibiusa runs off Usagi is adamant about finding her, sure that she's a new enemy since she's just received a pretty powerful premonition about the Black Moon family (she can detect her stalkers even from far away!). Usagi and Mamoru find Chibiusa sitting alone and destitute on a park swing, looking as if she hadn't a friend in the world and Mamoru, being the Prince of Neatness and Niceness, is charmed and wants to take her home and love her forever. Aww. She refuses adamantly to answer any questions about her connection to to the ginzuishou, so they decide to take her back to Usagi's house to keep an eye on her.
Usagi probably considered this the greatest mistake of her life, at least for a little while, because once Chibiusa arrives at Usagi's house Luna P comes out and the real fun begins. Chibiusa hypnotizes everyone in the house except Usagi to believe that she's a cousin visiting from far away. Clearly, Usagi is not impressed, but there's not much she can do about it, so Chibiusa is tucked away upstairs to sleep.
The next day there's some speculation on Chibiusa's origins between the girls that would make any fanfiction writer drool. Rei thinks that Chibiusa is Usagi's illegitimate daughter, while Ami thinks she must be Usagi's long lost sister. Only you and I know the truth, at least for now.
A little later, Usagi is gearing up for TA Academy's School Festival where Rei will be helping out the school's psychic club rather against her will (sucker). Usagi doesn't want to take Chibiusa along, so Ikuko-mama offers to take her shopping. Of course, as soon as Usagi frolics off to the festival, Chibiusa gives Luna the slip and frolics off after her.
Well, strange things are afoot at the festival courtesy of Cooan playing fortune-teller and a bunch of Black Moon goons dressed as the Catholic nuns. Kinky. The Sailor Senshi spank her with the assistance of Sailor Moon's new Cutie Moon Rod, but Rubeus arrives just in time to abduct Sailor Mars. Around the time that Rubeus makes off with Rei, the gang realizes that Chibiusa is standing there and watching open-mouthed. Usagi immediately accuses her of being in cahoots with Rubeus and his crew and she gets distressed and runs off, but not before Usagi spots a ginzuishou on a chain around her neck along with a key. What, are they giving them out as fair prizes? It's just not special having something defined as 'mysterious' when someone else has one too!
Chibiusa runs off and Usagi goes home alone feeling pretty guilty. Luna fetches Mamoru and takes him to where Chibiusa has gone to sleep in the middle of a parking lot in the rain. Mamo-chan takes her home. During a dream it is revealed that she has come from some shiny crystal place looking for help from Sailor Moon because something terrible has happened at home. Oooh, mysterious. Chibiusa wakes up and there's some cute father-daughter bonding and then Chibiusa introduces Mamo-chan and Luna to Luna P who calls her 'Small Lady.' Curiouser and curiouser. The key around her neck is revealed to be very important. Chibiusa says she'll need it to get back home, although she's unsure how to describe where she's from. She's a smart kid and “Far away, yet very close” is a good way to describe it if you're in the city of your birth a thousand years in the past.
Mamo-chan delivers Chibiusa back to Usagi the next morning and seems to have bonded a bit with her after having affirmed the idea that Sailor Moon is invincible. Mamo-chan comforts Usagi and seems to lay a few of her fears about Chibiusa aside, although she is still apprehensive.
(On a cute side note, it is here when Motoki is finally let in on the big secret about the identities of the Sailor Senshi. It's about time, since their command center is under the arcade XD).
More of the plot not involving Chibiusa directly is revealed, and Saffir and Demand are both introduced and Beruche is sent to make a play for the ginzuishou and remove Ami from the board. She shows up, claims to be a world famous dowser and chess champion and challenges Ami to a chess-match on television but then goes nuts and yanks off her sensible clothing to reveal her wacky blue lingere. She claims to be after “the Rabbit.” Ah, Chibiusa has so many endearing nicknames.
In any case, Ami is abducted just like Rei, although the remaining senshi spank Beruche until she expires. Chibiusa has now watched Sailor Moon loose two of her soldiers and is now beginning to doubt what Mamo-chan told her about Sailor Moon being invincible. Maybe no one can help her poor mama ;_;. Chibiusa is more confused and upset than ever.
Later that night back at the Tsukino residence, Usagi is crying over the abducted Ami and Rei when Luna P bounces out and tells her not to cry. Usagi freaks because the basketball just TALKED TO HER and prepares to whack it with a pillow. Chibiusa comes it an asks her not to hit Luna P and offers her the Tuxedo Kamen doll that Mamo-chan gave her during an earlier father-daughter bonding experience. Usagi freaks again because Mamo-chan has never given her anything like that, NO FAIR! Chibiusa rolls her eyes and takes her doll back, saying that she'd just come in to try and cheer Usagi up, although she apparently doesn't need it since she's going all freak-toaster. Usagi is just upset and high-strung over the fact that her best friends keep getting abducted right under her nose and she doesn't know what to do. Usagi feels a little more disposed to Chibiusa.
The next day at the arcade while the senshi busy themselves with senshi business (like how to get their comrades back) Chibiusa busies herself by getting the highest score ever recorded on the Sailor V game which somehow serves as the last bastion of crystal technology in the modern world. The senshi don't know what to think about this, but in order to keep her out of the senshi secrets on the game that she will eventually gain access to if she keeps playing, they distract her with a different kind of game where she can win candy. While they're talking she manages to rob the machine blind using Luna P, so Mamo-chan tells her that she's played enough games for the day and sends her frolicking home while the senshi go down into the control room to discuss serious business: namely, Chibiusa.
They realize that Beruche revealed that the Black Moon family aren't only after the ginzuishou, they're also after "the Rabbit" who the gang decides may well be Chibiusa. They're still not sure what to make of her, or even if they can trust her, since she won't talk to them.
Meanwhile, Chibiusa is walking home alone when it starts to rain. She changes Luna P into an umbrella. She doesn't appear to be worried about hiding her magical powers because some kid sees her. Luckily for Chibiusa, the kid's mom doesn't believe the kid's tall tales.
Chibiusa is really feeling lonely and wandering by herself in the rain, thinking of Sailor Pluto, magic powers, and her key. Mamo-chan catches sight of her as she rambles and goes up to her to try and comfort her. As he reaches for her hand a great roll of thunder peals and Chibiusa shrieks and Mamo-chan gets the strong psychic impression of a beautiful crystal palace under attack. He comforts Chibiusa as she stats to sob about her mother. Luna P lies on its side apparently short-circuited by Chibiusa's psychic distress.
Back at El Casa du Black Moon, Petz is sent to wreak havoc and catch the Rabbit if she can. Demand is revealed to have a creepy obsession with Neo Queen Serenity.
Mamo-chan puzzles over how he's supposed to repair Luna P when he doesn't even know how it works. Oh nuts, if only Ami-chan were here! Mamo-chan and Usagi discuss Chibiusa at the Crown and Mamo-chan admits that he's decided for sure that Chibiusa isn't an enemy and Usagi admits that she's decided that she'll do her best to protect her. Luna pokes at the frazzled Luna P while Mamo-chan and Usagi are talking and the Crown is filled with noxious smoke. Good going, Luna XD.
Meanwhile Makoto is infected with Petz's brilliant plan, the Black Moon Virus. She calls for help, and Usagi and Minako arrive on the scene in time to see Makoto put up a noble fight and then get abducted. Venus and Moon punish the crap out of Petz, but it's too late and Makoto is gone. Sucks to be Usagi.