While traveling through the vast Pinwheel Forest between Nacrene City and Castelia City, Ash and friends intend to stay on the path so that they won’t get lost. But when they come across a Sewaddle with impressive battling skills, Ash runs off into the woods to go after it, with the rest of the gang in pursuit.
They soon lose track of Sewaddle, and they get lost in the process! Iris suggests climbing a tree to get a better view of the land, and up on a high branch, they discover Burgh, the Castelia City Gym Leader, who’s also a renowned artist. He’s been living among the forest Pokémon, trying to find inspiration in nature and get out of his creative slump. When Sewaddle reappears, Burgh tries to introduce Ash to it, which proves more difficult than the Gym Leader expected. Sewaddle soon finds itself in a dangerous predicament, and Ash springs into action and saves the Pokémon—and to show its gratitude, Sewaddle decides to join Ash’s team!
Burgh declares that Ash’s unselfish rescue of Sewaddle has inspired him. He bids our heroes farewell for the moment, but promises he will be waiting at the Castelia City Gym for Ash’s challenge. Back on the correct path, it’s off through the Pinwheel Forest and on to Castelia City, with a new friend—Sewaddle!
Ash, Iris, and Cilan enter the Pinwheel Forest. As they move through the beautiful forest, admiring the scenery and listening to Cilan talk about the dangers of going off the trail, they find themselves ambushed by a small Bug Pokémon, who swoops down from a tree with string from String Shot and attacks Pikachu. Pikachu, angry, readies a Thunderbolt as the bug swings in the opposite direction, smacking Ash in the face and dodging the attack. Pikachu ends up shocking Ash. The bug continues to attack Pikachu with a barrage of Razor Leaf, and then ends up latching onto Pikachu's head with a Bug Bite.
After regaining his composure from the zap he received, Ash gets up and finds out from his Pokédex that the bug is known as a Sewaddle. Ash decides to battle Sewaddle, but Sewaddle uses String Shot to wrap Ash in a ball of string. Pikachu uses Iron Tail to free Ash, and he has Pikachu attack Sewaddle, who instead flees. Ash and the gang take chase, with Ash now fired up to catch this Sewaddle, but Ash ends up tripping and landing face-first on the ground. Cilan and Iris catch up to him and they realize that they are lost.
However, Ash is determined to find the Sewaddle and Iris claims that she hears the voice of the forest, only to learn that it was Ash's growling stomach. Iris then claims that her sixth sense is leading her somewhere and eventually gets them even more lost. The trio reason that, if they get to high ground, then they might get a sense of direction. They spy a very large tree once they reach a high point on some gray cliffs and decide to go inspect the tree. Ash and Iris climb it, and end up finding a curled up cocoon. Cilan shouts at it, and it's not a Pokémon that pops out, but a human. His name is Burgh, and he's the Castelia City Gym Leader. They question why he was cocooned up, and he explains rather dramatically that he is living like an insect in order to gain inspiration for his art and the fact that he is in a slump and can't find any inspiration. It is revealed that Cilan is a fan of his as well.
Sewaddle swoops down and kicks Ash in the face again, hopping right onto Burgh's shoulder. Cilan starts making supper for the group as Burgh attempts to bond with Sewaddle by tapping heads with it. He and Sewaddle make an instant connection. Pikachu, Axew, and Iris all manage to connect with Sewaddle too. Ash is eager to try, but Sewaddle instead Tackles Ash and knocks him over. Sewaddle turns away, ignoring Ash as he tries to talk to it.
Ash, Iris, and Burgh head out into the forest with Sewaddle, where Sewaddle stops in the middle of it. Iris thinks that Sewaddle is listening to the forest, but it is revealed that Sewaddle was just looking for the right fruit to eat. Later, Sewaddle stops in the middle of a field and wraps itself up and takes a nap. They all lay around it, staring into the day sky. Suddenly, Sewaddle wakes up. It walks toward a group of bushes, taking fruits off of them. A Woobat appears, and ends up calling another Woobat to join it. They attack Sewaddle, but Ash is attacked instead, taking the hit for the little bug. Sewaddle and Pikachu then team up to scare off the Woobat.
At sunset, the three of them return to the big tree with Sewaddle, where they find Cilan's supper of fruit salad ready for them. That night they ready themselves for sleep and Burgh asks Ash how much he has discovered since he started his Pokémon journey, and they all talk about how amazing Pokémon are. Sewaddle strings itself up by Ash in the tree, dangling there to sleep. Ash lies down, with Pikachu in his sleeping bag, but Sewaddle wakes him up by climbing inside too. Burgh comments on how unusual that is. The next morning when he wakes up, Ash instantly notices that Sewaddle is missing. He checks through the trees, and sees that a still asleep Sewaddle is being taken away by a Patrat. Sewaddle wakes up and tries to swing away, but is scooped away by the wind, and ends up accidentally attaching itself to a Deerling. The startled Deerling charges into the forest while Ash, Iris, Cilan, and Burgh rush after the Patrat.
They end up in a cavern where the Patrat meets up with its companion, another Patrat, who is sick. The Patrat was originally carrying Sewaddle back to the den to cure the other Patrat, because Sewaddle leaves have healing properties. Burgh heals the sick Patrat, but it finds the medicine bitter, but immediately begins feeling better. After leaving the cavern, the group sees Deerling, with Sewaddle still attached, charging toward them. Sewaddle's leaves are extremely tattered from all the running Deerling did, and it manages to detach itself from Deerling just as it's about to jump over a chasm, but ends up being blown toward a chasm with a crashing stream below it.
Ash dives after Sewaddle, but finds himself and Sewaddle unable to escape the current before reaching a waterfall so he decides to curl up in a fetal position to protect Sewaddle. Bracing for impact, Ash is surprised to find himself end up on land, pulled to safety by the String Shot of Burgh's Leavanny. Returning to the forest, Burgh's Leavanny manages to sculpt new leaves around Sewaddle's head. Sewaddle rubs his head on Ash's leg lovingly, and Ash makes the conclusion that Sewaddle wants to be caught. Ash tosses a Poké Ball, and catches Sewaddle. Once the capture is complete, however, the Poké Ball instantly shrinks down in size and locks with a glowing red light. Ash is confused until Cilan reminds him he already has a full party of six Pokémon, so he will need to deposit one of them if he wants the Poké Ball to unlock.
They arrive at a Pokémon Center at sunset, and Ash leaves one of his Pokémon with Professor Juniper so he can have his newly-caught Sewaddle on his team. Ash lets Sewaddle out, and the two successfully touch heads, having bonded. Burgh exclaims happiness, because Ash and Sewaddle touching heads has given him an idea for his next project. He then bids the group farewell, but not before telling Ash that he'll await his challenge at Castelia Gym.