Ash takes on Tony in his latest World Coronation Series match. Tony's Electabuzz uses Thunder Wave to stun Ash's Riolu before scoring a direct hit with Electro Ball. Ash cheers Riolu on, which encourages it to stand back up to its feet. Tony calls for a final Thunderbolt, though his chances of victory are dashed by Riolu's Vacuum Wave. Drone Rotom officiates the victory, changing each Trainer's ranking as a result – with Ash climbing from 921 to 901. Ash declares that he is on a roll and announces that he will use Riolu in his next challenge, much to the disappointment of Pikachu.
Arriving back at the Cerise Laboratory, Pikachu watches on as Ash has Riolu practice its battle techniques against Farfetch'd. Riolu defeats Farfetch'd with a Force Palm. As Pikachu steps up to have his turn, his enthusiasm goes unnoticed as Riolu is pumped to continue on. Riolu trains into the evening, battling Goh's Farfetch'd and Beedrill. Ash turns to Pikachu, apologizing for not getting in any training, only to see Pikachu is fast asleep. As he tries to explain that Riolu was doing really well, Pikachu lets out his frustrations and gives Ash a jolt of electricity.
Unexpectedly, Delia arrives at the Lab, and she admits she decided to stopover after visiting a friend nearby. She prepares a lavish dinner for everyone, remarking that Professor Cerise has taken good care of her son. The Professor offers her the guest room for the night, and Delia accepts his offer. She also joins Ash, the Professor, Goh and Chloe for the meal. Afterwards, Ash sees that Riolu is still eager to train, so the pair rush to get some more practice in, much to Pikachu's chagrin. Delia admits this is just like her son. Attention soon turns to Pikachu, with Chloe deducing that he is unusually jealous. Delia kneels down to Pikachu's level, and reminds him that he will always be special to Ash, after all they have been together for some time. Goh asks how exactly did Ash and Pikachu meet. Delia explains that Ash was supposed to get his starter Pokémon the very morning of his tenth birthday, but he overslept. Ash rushed over to Professor Oak's Laboratory where he received the last Pokémon – Pikachu. She adds that it took some time before Ash and Pikachu truly got along. With that, the Professor suggests Delia get some sleep. Mimey, and a still upset Pikachu, offer to escort her to the guest room. Delia thanks Mimey for its assistance, so it leaves her be for the night. Pikachu, however, is still angry with Ash and is reluctant to leave Delia, so he leaps onto her pillow. Delia relents before singing a lullaby to help Pikachu get to sleep.
Pikachu wakes up alone the following morning, just in time to see Delia leaving the Laboratory to return to Pallet Town. Goh and Professor Cerise turn their attentions to data analysis. Pikachu latches onto his Trainer's leg begging for some attention, but Ash orders him to be patient while he train with Riolu again. Pikachu is distraught and rushes after Delia's car. Mimey gives chase and orders Pikachu return to the Cerise Laboratory at once, but Pikachu proves too stubborn. Mimey follows Pikachu, keeping him safe from oncoming traffic as they continue into the grassy outskirts surrounding Vermilion City. Later, the pair come to a raging stream, which Pikachu tries to swim across. Mimey is forced to jump in after Pikachu is caught up in the rapids, and manages to save him from harm. The two continue walking, eventually reaching a main road. After spotting a hitchhiker get a ride to Vermilion City, Mimey decides they will hitchhike back to Vermilion City as well. While Mimey's attempts to hail a passing car all fail, Pikachu's cuteness leads a female motorist to pull over and offer them a ride instantly. Finally feeling safe, Mimey and Pikachu fall asleep in the back of the truck. They soon reach a fork in the road, with their driver taking the right turn. Mimey awakens and realizes that they need the left turn to reach Delia, so he grabs Pikachu and jumps off to continue the journey on foot.
Pikachu grows increasingly weary from the walk, so Mr. Mime is forced to carry Pikachu on its back. They eventually find some food, with Pikachu finding a Lum Berry tree. A passing Spearow swoops in, however, and grab the Berry picked by Pikachu. Mimey uses Psychic to retrieve the Berry, though this only agitates the Spearow and its flock. Pikachu leaps to the rescue, zapping the Spearow flock and sending them off. As Mr. Mime smiles, injured and collapsed to the ground, Pikachu recalls a very similar scene when he and Ash were first attacked by a Spearow flock.
Mimey and Pikachu continue walking well into the night, where they reach the Ketchum residence. Pikachu, however, has since had a change of heart and decides to return to Ash in Vermilion City. A familiar voice calls out to Pikachu, which turns out to be Ash, who had traveled back home especially to meet Pikachu. He apologizes for making Pikachu feel neglected, declaring that Chloe scolded him for it. Pikachu accepts the apology, leaping into Ash's arms for a hug and to deliver a powerful Thunderbolt. Inside, Delia lets Pikachu know how worried she was for his safety before calling for everyone to enjoy a home cooked dinner. Having accompanied Ash, Goh vows to keep Ash out of any trouble. Delia is glad to hear it, and just as she is about to ask everyone to dig in, Ash and Pikachu are already scoffing their mouths full. Ash and Goh decide to stay the night. As Pikachu prepares to sleep, he rolls onto his back and orders Ash sing a lullaby. Ash obliges, and soon both he and Pikachu fall fast asleep.