Hello! This actually belongs more in the General SM Discussion thread so I'll be moving it there ^^

~Mystery

In the anime, Chibi Chibi was Sailor Galaxia's star seed taken a mind and form of its own after she set it free, knowing she was going to become corrupted by Chaos.

In the Manga, Chibi Chibi and Sailor Cosmos are the same individual. Sailor Cosmos is Sailor Moon from a doomed timeline, one where she fled the battle with chaos and her future as Neo Queen Serenity failed to form. She became ultimate in power, but only because she drifted aimlessly for who knows how long after running away. She traveled back in time and disguised herself as Chibi Chibi, to make sure the Sailor Moon we've followed throughout the series wouldn't make the same mistakes she did.

If you feel like reading through it, we have an old but great Theory thread Who is Sailor Cosmos filled with all sorts of theories about her.

I posted a theory elsewhere where I worked out a theory that Sailor Cosmos and the original Queen Serenity are actually one and the same person.

I'll have to dig through the threads to find out where I posted it, but I'll do so when I can.

EDIT: Here it is:

http://www.thegalaxycauldronforums.com/t133p60-theory-who-is-sailor-cosmos

Sailor Cosmos, was/is the ultimate of Sailor Moon.  Chibi Chibi is her star seed.