Who or What is Luna-P?
Luna-P was given to Chibiusa by Sailor Pluto. It was not only a protective device, but a remembrance of her dear friend Luna. It seems to be self aware and follows Chibiusa of its own will. Chibiusa can also use it to communicate to the other Senshi.
Luna-P follows various commands of Chibiusa. It can change it different devices depending on what she needs. Once it was used as an umbrella to hypnotize Usagi’s family members. In the anime she commanded Luna-P to use magic to create a going away gift for Ami.
Black Lady was also seen around Luna-P, since it wanted to stay near Chibiusa and protect her. In the anime it was seen as her only friend and it was used to attack the other Senshi’s. In the manga, however, she would abuse it and smack it away from her cursing it.
Chibiusa was so upset and wanted to help her friends, that in Act 28 of the manga, Luna-P turned into the Pink Moon Stick. This then allowed her to transform into a Sailor Senshi and this was her friend Senshi weapon.