A Plethora of Pikachu! (Japanese: 大量発生チュウ！ピカチュウのたに！！It's a Pikachu Outbreak! The Pikachu Valley!!) is the 91st episode of the Sun & Moon series, and the 1,030th episode of the Pokémon anime. It first aired in Japan on October 7, 2018, in New Zealand on January 8, 2019, in Canada on January 26, 2019, and in the United States on February 16, 2019.
Ash, Kiawe, and Mimo discover an amazing place called Pikachu Valley, home to the biggest group of Pikachu they’ve ever seen! Their Trainer is a major pika-fan named Pikala, who gives everyone a set of Pikachu ears and a tail, and insists that they all talk in Pikaspeak by adding “pika” to every sentence.
At first, Ash’s Pikachu seems to be a big hit with the ladies—but Pikala clarifies that they’re just offering their usual pika-greetings. Annoyed by this behavior, the boss Pikachu challenges our buddy to a battle, but Ash’s Pikachu wins—and then thwarts an attempt by Team Rocket to grab the whole group!
Mimo, Ash, and Kiawe arrive at Pikachu Valley and meet a Pikachu enthusiast named Pikala. She nuzzles Ash's Pikachu and identifies him as a Kantonian Pikachu because of his silky, smooth fur. Pikala gives everyone, including Rotom, a set of Pikachu ear headbands and tails before explaining the three promises needed to become a resident of Pikachu Valley. She then teaches the group the basics of the "Pikanese" language and gives them each a Pikanese name. After declaring their commitment to the Pikachu, the group enters Pikachu Valley. Kiawe soon finds a Pikachu-decorated van called the Pikachu House. He attempts to enter, but is stopped after two Pikachu jump out. Kiawe looks inside the van and is then knocked to the ground by a horde of Pikachu.
Everyone's attention soon turns to Ash's Pikachu, who finds himself surrounded by Pikala's cautious Pikachu. Curly, one of Pikala's female Pikachu, approaches Ash's Pikachu and exchanges a tail to greet him. The other Pikachu follow suit, and the attention begins to overwhelm Ash's Pikachu. He resorts to posing, but the act is not well-received and the female Pikachu quickly walk away. Pikala explains that Alolan Pikachu greet each other by sniffing and rubbing tails, and it is the females who approach newcomers first. The males soon sniff and shake tails with Ash's Pikachu. Suddenly, a large ring of electricity surrounds the group, which develops into a thundercloud. As a bolt of lightning strikes the Pikachu, Pikala explains that the static electricity created by the tail-rubbing helps the Pikachu maintain their silky coats and boosts energy levels.
Meanwhile, a familiar Mimikyu watches the group of Pikachu and begins to shudder in anger. Team Rocket watches on, and Jessie reveals that her Mimikyu came out of its Poké Ball by itself. While the trio are terrified by Mimikyu's seething aggression, James suggests that they use Mimikyu to create a choatic distraction while they grab Ash's Pikachu. Jessie likes the idea, but points out that it might be tough to identify which Pikachu belongs to Ash. She smirks and suggests that they steal all of the Pikachu instead.
Ash, Kiawe and Mimo admire Pikachu's velvet smooth fur. Mimo and Pikala are excited to see Curly seems to have fallen in love with Ash's Pikachu. However, Ash's Pikachu isn't enjoying the extra attention and resorts to running away but Curly follows. A bolt of electricity strikes Pikachu's tail, taking him by surprise. Another one hits just as Curly attempts to hand Pikachu a Lum Berry. The source of the attacks is soon revealed to be a Shiny Pikachu nicknamed the Boss. Pikala explains that the Boss has been interested in Curly for some time. Mimo is excited to see a clash between the Boss and Ash's Pikachu over Curly, but Kiawe is more concerned that his sister knows about love. The two males soon confront each other, and the Boss strikes Pikachu with his pompadour hairstyle. Curly manages to separate the pair. Just as Ash's calls back Pikachu, the Boss strikes him with a bolt of electricity and the conflict ensues. The Boss and Pikachu exchange electric attacks, summoning Pikala's other Pikachu to watch the duel unfold. Ash tries to call his Pikachu back, but Pikala intervenes and clarifies that it is an issue to be resolved amongst the Pikachu. Pikala explains that the first to bite the other's tail will be victorious.
The Boss makes the first move and rushes forward, but Pikachu sends out several sparks through his tail. The distraction almost works but the Boss manages to avoid Pikachu's sneaky attempt. The Boss uses Volt Tackle, but Pikachu jumps into the air and traps the Boss in an Electroweb. Pikachu slowly walks up to the Boss and bites down on his tail, earning himself the victory. In an act of good sportsmanship, Pikachu clears the Electroweb with his tail and helps the Boss onto his feet. The Boss grabs Pikachu's hand and hoists it up into the air to officially declare Pikachu as the winner. Curly runs out of the crowd and goes onto rubs her nose with both the Boss and Ash's Pikachu, causing the two males to blush. Just as the Pikachu begin to celebrate, Mimikyu appears amongst the group and quickly surrounds itself in an angry haze.
Pikala is thrilled to see a Pikachu cosplayer, but Rotom explains that Mimikyu is a Pokémon. Jessie, James and Meowth soon arrive on the scene and perform their motto with a Pikanese twist. Pikala is unaware of the threat and gives Team Rocket a pair of Pikachu ears and tails to welcome them to Pikachu Valley. The gesture leaves Team Rocket perplexed. Jessie twists her Mimikium Z on her Z-Power Ring, and she, James, Meowth and Wobbuffet perform a group Z-Move. The Z-Power passes onto Mimikyu who goes on to drape its cloth over the Pikachu and unleash the nightmarish Let's Snuggle Forevermove. Jessie maintains her Z-Pose to allow Mimikyu to maintain the move's full power and keep the Pikachu trapped, but she becomes concerned as Ash's Pikachu leaps into view. James and Meowth soon return with the Meowth balloon, and Wobbuffet retrieves Jessie as she continues to hold her Z-Pose. Mimikyu floats into the air with the Pikachu still trapped inside its cloth, and the new discovery thrills James. Just as Kiawe reaches for a Poké Ball, Pikala stops him. She pulls down one of her wrist bracelets to reveal her Z-Ring, equipped with a Pikanium Z. She and the Boss perform Catastropika. The surge of energy strikes Mimikyu, causing it to release the Pikachu, and Team Rocket are sent blasting off. Ashs Pikachu sends out an Electroweb, which breaks the fall of Pikala's Pikachu, and the Boss catches Curly in his arms. Elsewhere, Bewear manages to catch Team Rocket just before they hit the ground.
Ash is amazed by Catastropika, but Rotom explains that Pikachu would need to know Volt Tackle to use the Z-Move, meaning that Ash's Pikachu can't use it. Meanwhile Pikala is overjoyed to have her Pikachu returned safe and assembles them for a roll call to make sure all of them are present. Pikala calls out her Pikachu's names with a descriptive sentence for each one. Ash and his friends watch on but are soon concerned that the roll call make take till evening.
From this episode onward, the anime moves from its Thursday 6:55 PM time-slot to a Sunday 6:00 PM slot. This marks the first time the show has changed its airing day since returning to the air following the EP038 incident, over 20 years earlier.
This episode, like Pikachu's Goodbye (the first episode to air after the show switched from Tuesdays to Thursdays), also revolves around a location where a large number of Pikachu live.
The Japanese title's inclusion of "大量発生チュウ", which translates to "Infestation-chu" may be a reference to the title of the event in Japan where people in Pikachu costumes walked through the streets, "ピカチュウ大量発生チュウ", which translates to "Pikachu Infestation-chu".
This is the first time a species-exclusive Z-Move is mentioned to require a specific move in order to be used. This is revealed when Rotom says that, in order to use Catastropika, Pikachu needs to know Volt Tackle, which Ash's Pikachu hasn't had as a part of his current moveset since the Best Wishes series.
This episode marks the rare occasion where Pikachu gets a dubbed voice. Only Ash's Pikachu retains its Japanese voice.