A Race Back To Childhood (Japanese: セレナにおまかせ!? 激走サイホーンレース！ Leave it to Serena!? The Exciting Rhyhorn Race!) is the 7th episode of Pokémon the Series: XY.
The episode continues from where the previous episode left off, with Ash asking Serena what she'll do now. She pauses, unsure of how to respond. Before she can think of anything to say, Ash invites her to travel with him, Bonnie and Clemont, as it was thanks to her that he was able to defeat Viola. Bonnie and Clemont express their support for the idea and Serena happily accepts, immediately determining their route: they will head back through Lumiose City on the way to Ash's next Gym challenge. The group takes off on Serena's projected route, with Clemont lagging behind as usual.
On the way to Lumiose City, Ash muses that since they'll be passing through that city again, that maybe he should challenge the Lumiose City Gym again. Upon hearing this, Clemont begins acting strange and advises Ash against it on the grounds that there are a lot of Pokemon he has yet to capture in Kalos. Placated, Ash begins to search for some. Clemont asks Serena why she decided to go on a journey. Serena responds by taking a handkerchief out of her pocket, explaining she wanted to give it back after so long after Ash gave it to her a long time ago during Professor Oak's camp in Pallet Town.
The flashback appears to a shady forest in Kanto where a younger Serena is lost, looking for the rest of her group. She's suddenly scared by a rustling in the bushes, which causes her to fall and injure her leg. The rustling Pokemon is only a Poliwag, which quickly runs away. Scared by her surroundings and wanting to go home, Serena begins to cry as she laments that she didn't even want to go to the camp. At the height of her despair, she calls out for her mother. She hears another rustling in the bushes and leans back, afraid of what it might be.
Calling out for the Poliwag that ran by just now, a younger Ash emerges from the bushes and asks what Serena's doing. He introduces himself to put her at ease and asks her name in return, as well as to what the matter is. Serena sniffs that her leg hurts, to which Ash pulls out the same handkerchief the present Serena is returning. He ties it around Serena's leg as a bandage and calls it a good luck charm to put her further at ease. Serena whines that she still can't stand up. Standing up himself, Ash extends his hand to her and tells her "Never give up until the end", the very words Serena herself used to inspire him while he was training for his rematch with Viola. He takes her hand and pulls her to her feet, congratulating her on standing. Still holding her hand, he takes her back to the campsite as Serena looks at him in awe and wonder.
In the present, Serena continues to say she washed the handkerchief and kept it for a long time, and when Ash arrived in Kalos, she thought it would be a good return gift. She tells Ash she saw him on television during the Garchomp incident. Ash suddenly lights up, now remembering Serena. (While he refers to her as the "straw hat girl," she doesn't seem to mind, and even blushes in response.) Ash is impressed that Serena ventured all this way just to return his handkerchief, and Serena explains that she also thought it would be nostalgic to see him again. She frowns at him not remembering her when they met, but Ash alleviates her feelings by apologizing. The happy atmosphere is suddenly cut short as a stampede cuts through their route.
The stampede turns out to be a bunch of Rhyhorn racers. As the racers depart, Officer Jenny arrives on the scene, reprimanding the gang for walking there as the path is closed to the public for the upcoming Rhyhorn race. She brings them to a town known for Rhyhorn races and explains how they work, and Clemont explains that Rhyhorn races are popular in Kalos. Serena explains that while there's tons of places dedicated to being race track, this is a very simple course. Ash is impressed by her knowledge of Rhyhorn racing and she reveals that she came in sixth place in Rhyhorn racing. Officer Jenny tells Ash that there is a Rhyhorn race tomorrow that he can take part in and asks if he's interested in taking part. Needless to say, he is.
At the Rhyhorn rental area, Jenny bids the gang goodbye as the rental lady explains to Ash that he gets to choose the Rhyhorn he wants to use in the race. Excited at the prospect of choosing, Ash starts to walk to the rear of a nearby Rhyhorn, but Serena tells him to stop, explaining that a Rhyhorn could get startled and run away if you approach it from behind and demonstrating the proper way to approach one: slowly, while facing it. When Clemont notices that Serena seems accustomed to being around Rhyhorn, she blushes and explains her mother taught her everything she knows as she was also a Rhyhorn racer. Ash asks Serena if she's trying to become a Rhyhorn racer like her mother which she denies, saying she wants to choose her own goal, although she doesn't know what it is yet. Ash then asks Serena if she would teach him about Rhyhorn racing. Told by Clemont it'd be good way for them to get to know each other and encouraged further by Bonnie, Serena agrees. (Hooray for peer pressure!) Through binoculars, Team Rocket resolves to steal Pikachu and the Rhyhorn. Later, Serena thanks everyone for waiting as she exits the building dressed in a pink racing suit (with a heart emblem she added herself). She asks how Ash is, and he's shown putting on a blue racing suit, which fits him well.
The first lesson is how to get on a Rhyhorn. Serena directs Ash verbally on how to do it and when he tries to get on, he fails. Miserably. Over and over. Serena demonstrates the correct way to do it, successfully getting on the Rhyhorn and signaling with her feet when she wants to start moving. Before she can explain how to start running, the Rhyhorn suddenly bucks her off. Landing on the ground, Serena's suddenly surrounded by Rhyhorn, and while she's afraid at first, she has nothing to fear as the Rhyhorn all start licking her. She realizes that these Rhyhorn are different from her mother's.
At the end of the day, Ash is still trying to ride Rhyhorn properly and Serena ends up giving him the same advice her mother gave her about not trying to talk lest you bite your tongue. She notes that Ash was able to do it even though it was hard, and begins to think she misjudged Rhyhorn races.
Late at night, Serena's in the kitchen with her Fennekin, making cookies. Fennekin wants to know what's going on, but Serena hushes it and tells it to keep it a secret from everyone.
The next day at the race, Ash gets off to a slow start behind the others. Meanwhile, James has his Inkay blot out the video cameras so that no one can see what Team Rocket's doing. They then proceed to capture all the Rhyhorn, including Ash's and manage to snag Pikachu as well, trapping Ash in a net. As Team Rocket moves out, the train of cages suddenly breaks down and Clemont's Bunnelby is revealed to be behind it. Clemont shows up in exhaustion and congratulates his Bunnelby for stopping Team Rocket. Serena and Bonnie show up as well and ask Ash if he is ok. Team Rocket picks themselves up, Fennekin taps Serena and tells her it wants to battle. Serena has it use Ember, which causes James to drop the remote. Clemont picks up a rock and smashes the remote, freeing Team Rocket's captives. The Rhyhorn quickly dispatch Team Rocket. With Team Rocket taken care of, everyone rejoices and Ash thanks his friends for saving him, Pikachu and the Rhyhorn. Moments later, Officer Jenny arrives and asks if everyone's alright. She frees the other racers who were captured.
Later that afternoon, Serena's friends introduce themselves to her mother over the phone and Serena tells her mother she's decided to travel with Ash. Grace agrees with this, thinking it will be good for her. A short while later, Serena gives everyone in the group their own little bag of cookies that she was baking that night.
- Serena is shown to be the new navigator and cook, marking the first time one of Ash's traveling companions fulfilled two roles, the two roles Serena's fulfilling being the regional girl (Misty, May, Dawn, Iris, etc.) and the navigator/cook, which is also the first time the latter role is taken on by a girl.
- In the flashback scene where Serena first meets Ash, he is chasing a Poliwag. This is a reference to the Pokémon Adventures manga in which Poliwag was Red's first Pokémon.