After having Plusle or Minun as your partner in Pokémon Ranger and having 17 possible partners in Ranger: Shadows of Almia, Guardian Signs has you return to having one single partner during the main game. This partner is the Ukulele Pichu.

The Ukulele Pichu is different from the normal Pichu you will encounter within the game. You will encounter it on Dolce Island where it will be leading a group of Pichu with its music. It is named the Ukulele Pichu by Booker based on its habit of carrying round a Ukulele. Capture it, and it will join you and always follow you like all ther partners in the past games.

Like some of the previous partner Pokémon, the Ukulele Pichu has a unique Pokémon Assist. This assist cannot be used by any other Pokémon but it is similar in several ways to some other Pokémon Assists within the game. When you send Pichu out into the arena, it will start playing its ukulele. This will create musical notes that, when the opponent hits it, do a small amount of damage. However, after a few seconds of that, Pichu will let out a massive electrical shockwave which will do massive damage. This will allow the Pichu to be even more devastating than anticipated.

Like the other Pokémon Assists, the duration and damage of Ukulele Pichu's Pokémon Assist can be increased by levelling up your Capture Styler with the Ranger Points accumulated within the game.

There is one drawback to the Ukulele Pichu. In the various parts of the game where you end up travelling back in time with Celebi, the Ukulele Pichu is unable to follow you and so remains in the area you left from until you return to the present. However, you are able to get new partners in the past which can only be in the past except ofr when you call them with a Ranger Sign in the present.