Luna-P was a device used by Chibiusa Tsukino that was given to her by Sailor Pluto. It was her dear friend and it bore a strong resemblance to Luna. In both the manga and anime versions, Luna-P seemed to have some self-awareness; it followed Chibiusa and defended her. She could also use Luna P for communication with the other Senshi. Luna-P appeared in episode 60 in Sailor Moon R.
Chibiusa used Luna-P with various commands. In the manga, Chibiusa used Abracadabra Pon, a phrase that was taught to her by Sailor Pluto, for whenever she felt sad. She also transformed Luna-P (in both the manga and anime) into an umbrella in order to hypnotize Usagi's family into thinking that she was their cousin. In the anime, Chibiusa used Luna P Henge (while she was in either civilian or Senshi form) to transform Luna-P into an object she desired. She also used Luna-P for Luna P Magic once, in which she used to create a gift for Ami, when she was going to study in Germany. She also used the attacks, Luna P Shouka(in the anime) and Luna P Attack (in two video games).
Black Lady's response to Luna-P varied between the anime and manga. In the anime, Black Lady viewed the device as her only true friend, and used it to attack the Sailor Senshi. In the manga and Crystal, however, Black Lady smacked it away, calling it a stupid and childish toy. In Act 28 of the manga and Crystal, Luna-P transformed into the Pink Moon Rod when Sailor Chibi Moon desired the power to help her friends.
In the musical "Pretty Soldier Sailor Moon S ~ Usagi - The Path to Become the Warrior of Love", Luna-P was portrayed by a helium-filled foil balloon, and was there referred to as Luna-P Ball.
In the video game Sailor Moon: Another Story, Luna-P was used as a save point and could be found in random places throughout the game.