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Partner Pokémon in Pokémon Ranger: Shadows of Almia
A Partner Pokémon (Japanese: パートナーのポケモン or パートナーポケモン Partner Pokémon) are the only Pokémon allowed to always accompany a Pokémon Ranger and do not leave after using a Poké Assist like other Pokémon. Combined, there are more than 20 Partner Pokémon in the three Pokémon Ranger games.
In the Ranger series
There are only two Partner Pokémon in this game; they are Plusle and Minun. The one which the player gets depends on their chosen gender, with males receiving Minun and females receiving Plusle.
Ranger: Shadows of Almia
The number of possible Partner Pokémon was greatly increased, now up to 17, one for each type, so the player would have access to a Partner Pokémon with every type of Poké Assist. The player encounters their first at Nabiki Beach, either Pachirisu, Starly or Munchlax. The two not chosen are obtainable later on in the game. Also, throughout the game, the player can obtain different Partner Pokémon by completing certain quests involving the Pokémon. However, Kricketot, Croagunk and Mime Jr. are obtained during the main storyline. The player is only allowed to take one partner at a time. The rest remain at Partner Farm.
Ranger: Guardian Signs
In the main storyline, players get to befriend a ukulele-playing Pichu on Dolce Island. The Assist of Ukulele Pichu gets several upgrades as players progress through the game. When playing in the past, due to the fact that the Ukulele Pichu stays in the present, players may choose as their Partner any Pokémon whose heart slate they have obtained from a temple. When first arriving in the past, players have a Piplup as their Partner.
In the anime
Solana's Plusle in the anime
In Solana's appearances in the Advanced Generation series, she was accompanied by her Partner, a Plusle. Plusle used status moves such as Helping Hand to assist Pokémon that Solana had captured. For reasons unknown, it was not seen in her appearnces in the Diamond & Pearl series.
The Ukulele Pichu is seen during Pokémon Ranger: Guardian Signs (Part One) and Pokémon Ranger: Guardian Signs (Part Two), but is not seen in Ben's appearance in in the main series proper.
In the manga
Pokémon Ranger the Comic: Double Mission
In Pokémon Ranger the Comic: Double Mission, Lunick and Solana are seen with their respective Partners, Minun and Plusle.
Darkrai Mission Story: Pokémon Ranger Vatonage - the Comic
In Darkrai Mission Story: Pokémon Ranger Vatonage - the Comic, Kellyn and Kate's Partner Pokémon are both Pachirisu.