The Pokémon anime is ed for a lot of things, but character development isn't usually one of them. While it may seem like Ash is a fairly static character, he's actually learned and grown quite a bit over the years.

Because the Pokémon anime is structured into "series" based on each game, which function as a sort of soft reboot between seasons, Ash often finds himself back at square one. That's pretty different from the usual shonen-style anime character progression, which is part of why Ash so frequently appears to be flat. However, Ash really has changed a lot throughout the series, going from a hot-headed young rookie to a cooler, more mature and skilled trainer by the end of Journeys. These episodes provoked major growth in Ash in many cases, or at least showcased a side of him fans hadn't seen before.

10 Arriving in Style!

Series: Pokémon Diamond and Pearl, Episode 86

Ash is normally all about Pokémon battles and rarely seems to think about anything else, but this episode showed an unusual side of Ash, as he’s convinced to take part in a fashion show known as the Hearthome Collection. Working with Brock, he comes up with a rather bizarre outfit, depicting himself and Pikachu as the Japanese storm gods Fujin and Raijin (who would later inspire the Pokémon Tornadus and Thundurus). Despite his bizarre appearance, Ash makes it to the final round of the contest, and ultimately wins a prize for originality, although not the grand prize.

Despite Ash’s obsession with Pokémon, he’s often willing to give new things a try, even if they are outside his interests. This episode is perhaps the best example of that, with Ash enthusiastically diving into fashion, even if his ideas are a bit outside the norm.

9 Til We Compete Again!

Series: Pokémon XY, Episode 140

The final episode of XY sees Ash parting ways with his traveling companions for the past 140 episodes. That includes Serena, who has had a severe crush on Ash for almost the entire series. Serena gradually realizes that they really are parting ways and may not be able to see one another again for quite a long time, so as she’s about to leave, she turns around and gives Ash a surprise kiss, shocking Clemont, Bonnie, and Ash himself. It’s definitely a big moment for Serena, but this is also a huge scene for Ash.

Ash is rather contemplative in this episode, thinking back on all the things he experienced in Kalos and all the people that he met. Usually someone who always lives in the present, it’s interesting to see Ash reflecting on what’s happened, and fully appreciating his experiences.

8 Bye Bye Butterfree

Series: Pokémon The Original Series, Episode 21

Early in his journey, Ash comes across a flock of Butterfree which are engaged in their mating season. He’s excited to allow his Butterfree to participate, and works hard to help Butterfree find a mate, particularly focusing on impressing a Pink Butterfree. While their attempts are initially met with resistance, Team Rocket attacks and begins capturing the Butterfree. Ash orders his Butterfree to attack them and help free the others, finally making an impression. After successfully defeating Team Rocket, Ash realizes that he must say goodbye to Butterfree so that it can go off and mate. It’s a tearful farewell.

This is one of the first episodes where Ash actually begins to think about his Pokémon’s needs before his own. Ash doesn’t want to lose Butterfree, but it’s important that Butterfree be allowed to do this, and in the end, Ash does what is right for Butterfree, even if it hurts.

7 Charizard's Burning Ambitions

Series: Pokémon The Original Series, Episode 134

This episode is similar in many ways to “Bye Bye, Butterfree,” in that it involves Ash leaving behind a Pokémon for its own good. Like Butterfree, Ash’s Charizard finds a valley full of other Charizard, including a female one named Charla. However, Ash’s Charizard is regarded as a weak runt, and is dismissed by the others. Team Rocket once again makes an appearance (although this time to deliberately help Charizard) and by fending them off, Charizard wins approval. Charizard stays in the valley, vowing to become stronger and reunite with Ash some day.

Once again, Ash realizes that what’s good for his Pokémon isn’t the same as what he wants, and is forced to make a choice. Unlike Butterfree, though, Charizard will return to help Ash on several occasions, proving that Ash was right to leave him behind for training.

6 Evolving Strategies!

Series: Pokémon Diamond and Pearl, Episode 132

Throughout Diamond and Pearl, Ash has had a rivalry with a cruel trainer named Paul, which comes to a head in this episode (and the previous) with a full battle at Lake Acuity. Ash and the Chimchar that he got after Paul abandoned it work hard and fight well, but in the end, it’s not enough, and when all is said and done, Paul emerges victorious, looking down on Ash even more than ever before. Ash is devastated by this loss, and it leaves him reeling.

This is an interesting episode in that Ash didn’t make any critical errors in battling that led to his loss; he did everything right and it still wasn’t enough. It’s a tough lesson for Ash to learn, especially against a rival like Paul, who takes his victory as affirmation that his cruel training techniques are effective.

5 Can't Beat the Heat!

Series: Pokémon The Original Series, Episode 270

Moving from one rival to another, this episode centers on Ash’s climactic battle with Gary in the Johto League. Ash uses his outside the box thinking when it all comes down to Charizard vs. Blastoise, and manages to overcome the type disadvantage by heating the ground and causing the battlefield to be cloaked in steam. Ash defeats Gary, shocking his long-time rival. They meet up later that night at a nearby lake, and Gary its that in the past, he couldn’t tolerate losing to Ash, but now, he sees Ash has defeated him fairly. Ash is eager to bury the hatchet.

This marks a major turning point for Ash and Gary, now friends instead of just rivals. Gary is humbled by the experience, but what’s really notable is Ash’s behavior. He doesn’t gloat, like he might have a hundred episodes ago, but is understanding and willing to forgive, a real sign of maturity.

4 Snow Way Out!

Series: Pokémon The Original Series, Special Episode

Ash, Misty, and Brock forge ahead in a snowstorm, but Pikachu gets lost, and Ash rushes off to find him alone, losing Misty and Brock in the process. Ash manages to find Pikachu, but they have no way to locate their friends, and must hunker down where they are. Ash creates a small cave in the snow to get out of the storm, and goes to great lengths to ensure his Pokémon are comfortable, even taking off his own jacket to give their Poké Balls extra warmth. His Pokémon emerge from their balls to warm him, and they weather the storm together.

Despite being a rather early episode, this showcased how much Ash had grown already, putting the Pokémon he is responsible for first, even above himself. Ash is characteristically reckless in his search for Pikachu, but nothing proves how deeply he truly cares like the snow cave scene.

3 Seeing the Forest for the Trees!

Series: Pokémon XY, Episode 121

Having suffered a devastating loss at the hands of gym leader Wulfric, Ash is in a funk, and isn’t interested in spending time with his companions. After getting into a fight with Serena, he goes out alone to the woods to think, but becomes lost as a snowstorm sets in. Taking shelter with some wild Pokémon, Ash sees some Spewpa that were unable to make it out of the storm and decides to help them. When that winds up with Ash in danger, Greninja appears, easily taking on its Ash-Greninja form and saving him.

This episode involves Ash revealing some backstory about himself, relaying an incident to Greninja which inspired his original love of Pokémon. The similarities between that incident and this one reignite his ion, and Ash manages to shake off his funk and resolve to try even harder in the future.

2 Battling a Thaw in Relations!

Series: Pokémon Diamond and Pearl, Episode 188

It’s not just time for Ash to have his rematch with Paul—this time, they’ll be facing off in the Sinnoh League, with their place in the tournament on the line. Both Paul and Ash have grown far stronger than they were the last time they fought, and the battle is hard fought on both sides. In fact, as the battle goes on, it becomes obvious that Paul is gaining some respect for Ash’s skill, seeing him as a valid rival for the first time. It all comes down to the wire, but Ash emerges victorious, proving his training method superior.

Once again, Ash shows comion for his rival instead of seeing him as just an enemy. While Paul doesn’t appear much after this, there’s a distinct change in their relationship to one of mutual respect, something that Ash worked hard to earn.

1 The Rainbow and the Pokémon Master!

Series: Pokémon Journeys, Episode 147

Following a brief reunion with Brock and Misty, Ash returns home alone to Pallet Town, where he soon runs into Gary. Gary congratulates Ash on winning the World Coronation Series and becoming a champion, but asks him if that makes him any closer to being a Pokémon Master. Ash isn’t sure what to say, and spends much of the episode contemplating the question. What does it mean to be a master? Ash, in an unusually thoughtful way, decides that it means befriending every Pokémon, and that he’ll keep chasing that impossible goal.

As the final episode for Ash, it was a lot more contemplative than most were expecting. Ash is forced to do some serious introspection as a result of Gary’s question, and realizes that while he loves battling, that was never the end goal. Ash realizes he had been chasing tournaments and titles as if that alone would achieve his goal, but while it helps, that was really beside the point. For these reasons, this may be the deepest episode of Pokémon featuring Ash Ketchum.