In the region of Oblivia, a gang of thieves known as the "Pokémon Pinchers" are stealing wild Pokémon and planning to use them for their own nefarious purposes. Two Pokémon Rangers, Summer and Ben, are sent to investigate. However, after an encounter with the Pinchers, one of them is kidnapped while the other is left stranded on an island. There they meet a Pichu with a ukulele, who teams up with them to help rescue its Pichu friends who have also been captured by then Pinchers. Can you rescue your partner, and save the Pokémon of the Oblivia region?
Pokémon Ranger: Guardian Signs is the third in the Pokémon Ranger series. As with the previous games, you move your character around using a device known as the stylus, as well as battling with a device called the "capture styler" (represented by the stylus). To battle, you encounter a Pokémon on the touch screen, and your aim is to repeatedly draw connecting loops around it until you deplete its health to zero, allowing it to join your team. Pokémon can be used in the environment to clear obstacles and help you progress (such as such as cutting trees, extinguishing fires and so on), or by assisting you in battle and helping you weaken enemy Pokémon. Near the start of the game, Ukulele Pichu becomes a part of your team and randomly appears during battles to assist. If you tap it when it appears, it will jump into battle and play its ukulele, which scatters musical notes around the screen which weaken enemies.
A little bit further into the game, you also gain the help of the Legendary Pokémon dogs, Raikou, Entei and Suicune, first introduced in Pokémon Gold and Silver. These Pokémon have special abilities that allow you to reach places that you normally couldn't (for example, Raikou can leap across large gaps). To summon these Pokémon, you must draw a special sign with the stylus that represents them, but these can only be drawn outside where the sky can be seen.
After a key point in the game, you also unlock the ability to travel back in time with Celebi, which gives you access to wireless multiplayer Pokémon Ranger missions. These missions can be played with up to four players, and Rangers can team up to help capture Pokémon more quickly. This is a great help as each mission must be completed within a certain time for it to be a success. Most wireless missions can also be played solo, but are more difficult this way. You can also earn experience which can be used to increase your capture styler's power, health and speed.