Satoshi, Hikari, and Takeshi's Pokémon are spending the day together in a city lot where a swing, seasaw, tires and a large slide is located. Most of the Pokémon jump off the slide into Torterra's tree but Pikachu and Pochama overshoot it and land in a pile of tires. While trying to get up, one of the wheels starts spinning with Pochama in the tire and Pikachu on top. They roll down the cordor and crash at the end of it.

Pikachu and Pochama who are recovering from their crash, look up into the sky to see a bright light. Suddenly an Unknown falls from the sky and lands on the tire. The Unknown seems confused and doesn't know where it is. While talking to Pikachu and Pochama, Rocket Gang Nyarth, Sonansu and Manene spot them and begin to listen to the conversation.

An Eneco then shows up and is surprised to see an Unknown. It thinks it knows a way to help Unknown get back to its realm as it remembered seeing a similar looking light. Pikachu, Pochama, and Unknown follow the Eneco who takes it to the underground sewers. Rocket Gang Nyarth realizes that if they capture the Unknown they will have unlimited money and he schemes with Sonansu and Manene to capture it and they follow Unknown. Takeshi's Gureggru had been hiding behind a wall and noticed the whole situation and decides to follow Rocket Gang.

Eneco leads them to a dead end with three block shapes in the wall. It presses the first extruded block which activates a glowing line to the next block which then pops out. Pikachu presses the next block which activates the final block just at Nyarth arrives. He tells them he's there to capture Unknown and jumps at it. Instead of catching the Unknown, it hits the final extruded block. The wall begins to glow and then sucks all the Pokémon through the portal.

They arrive in a new realm that looks like Tetris blocks. They decide to cross to the other side. Pochama decides to go a different direction but ends up falling but loops back and lands back where it started. It then decided it was best to follow Pikachu and the others. Nyarth decides to follow them but they encounter the singing Maril who had tormented them in the past. It puts them to sleep and they fall off the blocks back to the beginning of the realm.

On the other side, Pikachu, Pochama, Unknown and Eneco find another portal and are then followed by Rocket Gang, Maril and Gureggru again. This time Nyarth, Sonansu and Manene are mega sized and Pikachu, Pochama, Unknown and Eneco are their regular size. Nyarth begins to chase after them until another portal sucks them off to another different realm. In this new area, Pikachu is now mega sized while Rocket Gang are their normal sized selves. Rocket Gang ends up on Pikachu's head and Pikachu begins charging his Thunderbolt. Nyarth tells Pikachu to stop otherwise they'll be permanently paralyzed from the shock. Manene uses Teeter Dance to stop Pikachu and the others. Rocket Gang are sent flying off Pikachu and land near a mega sized Maril who once again uses Sing to put them asleep.

Pikachu and friends then encounter the legendary lake Pokémon Yuxie, Emrit and Agnome who end up giving them each an apple to each. Rocket Gang finds a bunch of berries nearby but they mistake the ball at the end of Maril's tail as an Oran Berry. Maril puts them to sleep with Sing once again. Pikachu and the others continue their journey and find a new area with many blocks twisting up in the air like a tornado. They start to climb on the blocks but end up falling. Deoxys comes to rescue them and takes them to the top. At the top are all of the Unknown. Two Unknown come to visit the Unknown that had been traveling with Pikachu and his friends. They are finally reunited. Unknown thanks them for their help and then shows them the portal that leads them back to the city and their friends. Pikachu, Pochama, Eneco, Rocket Gang and Gureggru jump into the portal and return to the city. They end the day by watching a fireworks display.