Oshawott's debut appearance
As a Pokémon available for use at Professor Juniper's lab
Oshawott originally belonged to Professor Juniper, as one of the three starter Pokémon a new Pokémon Trainer could choose. Ash thought he was cute when he was sent out in In The Shadow of Zekrom!, when Trip had to decide between the three starters. Oshawott was extremely shocked when Trip chose Snivy, but quickly got over it and started taking interest in Ash; observing him but staying out of sight, and to the point that he left Professor Juniper's lab to follow him.
Oshawott appeared again in Enter Iris and Axew and used his scalchop to rescue Ash's Pikachu and Iris's Axew from the clutches of Team Rocket. He later battled Jessie's Woobat briefly before Team Rocket escaped.
Eventually, Oshawott expressed interest in traveling with Ash and convinced Ash to take him along on his journey in A Sandile Gusher of Change!. Ash only realized that he was Professor Juniper's Oshawott when he failed to capture him in a new Poké Ball, and had to obtain a worried Professor Juniper's approval to allow Oshawott to travel with him and to request for Oshawott's Poké Ball. She permitted Oshawott to travel with Ash, but Oshawott had disappeared by the time Ash received his Poké Ball. After nearly falling into boiling hot water, Ash saved Oshawott by successfully returning him to his Poké Ball.
In Triple Leaders, Team Threats!, Oshawott was then used against Ash's Pokémon in his third Striaton Gym battle against Cilan and went up against Pansage. This surprised Iris, who thought he should use a Flying-type like Pidove instead. Though initially confident, he got scared by Pansage and had to be pushed into battle, but was convinced by Ash to battle Pansage. His Tackle was dodged and was hit by Pansage's Bullet Seed, he was bitten on the head by Bite and whilst running, crashed into a wall. He used multiple Water Gun attacks but they were all dodged execpt the last one. Oshawott was shown to be tired whilst attacking. Pansage then proceeded to use Solar Beam and then fired it at Oshawott. In Dreams by the Yard Full!, Oshawott used its Scalchop to deflect Solar Beam, surprising everyone. He then deflected Pansage's Bullet Seed with his scalchop as well, he then went for a Razor Shell, but Pansage countered with Bullet Seed knocking his scalchop, he then used Bullet Seed to prevent Oshawott from retrieving his Scalchop. Cilan then performed an evaluation, criticizing Ash and his Oshawott, but praising his Pansage in comparison. Ash then had Oshawott use Water Gun of a wall, bouncing it across rocks, hitting his Scalchop and throwing it into the air, Oshawott then caught it and hit Pansage with Razor Shell. Then his Razor Shell went up against Pansage's Bite, knocking out the Grass Monkey Pokémon and earning Ash the Trio Badge.
Oshawott was revealed to be male when he battled a wild female Snivy that would be caught by Ash in Snivy Plays Hard to Catch!. He became infatuated when hit by Snivy's Attract, and was eventually recalled.
In A Rival Battle for Club Champ!, he was used to fight against Trip's Tranquill. He was defeated by two quick and consecutive hits of Aerial Ace, due to Tranquill's Super Luck Ability, which increased Tranquill's chance of inflicting critical hits.
In The Battle According to Lenora!, he battled Lenora and her Watchog after her Lillipup's Roar pulled him onto the battlefield, to his surprise. Despite fighting well and making use of his scalchop as a shield again, he was defeated by a powerful Thunderbolt after Watchog separated him from his scalchop. In Rematch at the Nacrene Gym!, Oshawott trained with Ash in the Battle Club to increase their speed and power. They trained in a wave pool and after Iris's Axew messed with the controls, Oshawott learned Aqua Jet, but had trouble with hitting the target. He battled Watchog again in Ash's rematch with Lenora after being pulled into battle again by Roar. He still showed some difficulty in controlling Aqua Jet, but he managed to hit Watchog on his third try. Unfortunately, he also knocked himself out in the process after taking a lot of damage from Watchog's Thunderbolt and Confuse Ray attacks, leaving Ash's Tepig to battle Lenora's Herdier alone.
In Emolga the Irresistible!, Oshawott developed a crush on a wild Emolga. When she used Attract on Bianca's Minccino, Oshawott voluntarily jumped in the attack's path so he could get hit with it instead. Later on, he decided to go up against a group of Swoobat to protect Emolga. However, he was soon defeated by a powerful Charge Beam. On both occasions, Ash was forced to recall Oshawott to his Poké Ball. Later in Emolga and the New Volt Switch! he valiantly protected Emolga and Axew from some wild Watchog and retrieved them an apple each, however, a wild Simisear knocked him out, despite Emolga hardly caring.
Oshawott without his scalchop
In Oshawott's Lost Scalchop! Oshawott battled against Stephan's Blitzle, where his scalchop ended up getting kicked out of his hands and off into the distance. Horrified, Oshawott chased after it but, alas, he could not find it. After many failed substitutes, Cilan's Dwebble crafted a new scalchop out of a nearby rock but it ended up being too big and too heavy for Oshawott. Ash then trained him, giving Oshawott the strength to carry the new scalchop. Unfortunately, it ended up being destroyed during a rematch with Blitzle, but Oshawott turned out to be much faster because of all the training and was able to defend himself without a scalchop. He soon defeated Blitzle with a lucky-shot Aqua Jet that sent them both crashing into a boulder. After the battle, Axew found the missing scalchop in the forest and returned it to Oshawott.
In Ash and Trip's Third Battle!, Ash sent out Oshawott to battle Trip's Timburr. Ash commanded Oshawott to use Aqua Jet, which went out of control again. When Oshawott tried the move again, Trip took pictures of him. Trip called a time-out and then showed Ash pictures of Oshawott's face, and revealed that Oshawott's eyes were closed whenever he used it. Trip suggested that was why Oshawott had so much trouble controlling Aqua Jet. The battle resumed, and while both Pokémon used their "weapons" to full extent, Oshawott won out over Timburr using Razor Shell. Following Trip's advice, Ash trained Oshawott to open his eyes under water in Facing Fear with Eyes Wide Open!. Oshawott was at a major disadvantage to a group of Tympole that attacked him while his eyes were closed, eventually, Oshawott opened his eyes and scared off the Tympole. Later when battling the Palpitoad that ordered the first attack, Oshawott executed a perfect Aqua Jet, defeating him and enabling Ash to catch him.
In A Call for Brotherly Love!, Oshawott was used in a battle against Chili's Pansear. After Oshawott volunteered to battle with Pansear, Ash decided that it was a good idea, and the battle commenced. Although Oshawott battled well, hitting Pansear with several powerful Razor Shells, Pansear proved to be too strong and defeated Oshawott with its newly learned Solar Beam.
In Battling the King of the Mines!, Oshawott was Ash's first Pokémon in his Driftveil Gym battle against Clay, he went up against his Krokorok, Oshawott used Aqua Jet but Krokorok used Dig causing him to crash into a wall, Krokorok then used Sandstorm knocking back Oshawott and creating a Sandstorm, blinding Oshawott as he got sand in his eyes, Krokorok then hit him with its Bite, he then attempted to use Razor Shell but was blinded again causing the attack to go nowhere, after being hit by a powerful Stone Edge, Ash got Oshawott to use Water Gun on the field stopping the Sandstorm and getting the sand out of his eyes, allowing him to see. Krokorok used Dig but Oshawott aimed Water Gun into the hole, dealing damage and forcing Krokorok to emerge, he then used Aqua Jet to hit Krokorok and defeated the Desert Croc Pokémon with his Razor Shell. He then went up against Palpitoad, which was more powerful than Ash's Palpitoad, Palpitoad used Hydro Pump whilst Oshawott used Water Gun, but his Water Gun was easily overpowered by Hydro Pump causing him to crash into a wall, he then went for a Razor Shell but was countered by Sludge Bomb, hitting Oshawott and separating him from his Scalchop, this distracted him, allowing the Vibration Pokémon to defeat Oshawott with his Rock Smash.
Oshawott and his rival, Dawn's Piplup
In All for the Love of Meloetta! he met Meloetta and subsequently fell deeply in love with it. To his excitement he was left to watch over it, while Ash and Pikachu left to get more ice. From nowhere, Emolga, who had brought an Oran Berry for Meloetta, crashed into Oshawott and the two began fighting. They calmed down when Ash and co returned and Meloetta began to sing. subsequently in Piplup, Pansage, and a Meeting of the Times!, he fell for Dawn's Buneary, but soon forgot her when she embraced Pikachu and Meloetta revealed herself. When Dawn's Piplup fell for Meloetta just as Oshawott had before him, Oshawott attacked him with Aqua Jet, upset to see Piplup and Meloetta getting along, sparking a rivalry. In the next episode, when the gang were surrounded by Onix and Meloetta appeared frightened, both he and Piplup heroically battled the Onix. Eventually, when surrounded by the Onix again, Oshawott learned Hydro Pump to fight them off. In Goodbye, Junior Cup - Hello Adventure!, Oshawott confronted Piplup over Meloetta one more time before Piplup and Dawn left for Johto, their contempt soon turned into sadness and they bid a teary farewell.
In Meloetta and the Undersea Temple!, Oshawott was training with Pansage, which inspired Meloetta. After transforming into her Pirouette Forme, she insisted that she may train with Ash and Oshawott. However, intimidated and reluctant to fight the object of his affections, he refused to battle. In Unova's Survival Crisis!, Oshawott bid a teary and final farewell to Meloetta, at the aid of Pikachu's comfort.
In Cameron's Secret Weapon!, Ash sent Oshawott out as his second Pokémon in his Vertress Conference battle against Cameron and his Hydreigon. Despite of the notable size difference, Oshawott proved to be a reasonable opponent for the Brutal Pokémon, right away scoring a hit with Aqua Jet. However, Hydreigon was able to avoid Oshawott's following Razor Shell before striking back with Dragon Pulse. Despite of the hit, Oshawott went on with another Razor Shell, which eventually hit one of Hydreigon's heads. Using the moment it took from Hydreigon to recover from the hit as his advantage, Oshawott used Hydro Pump, which scored a direct hit on the Brutal Pokémon. Hydreigon then fired a Tri Attack, which Oshawott was unable to block, taking more damage. Oshawott fought back with Tackle, but his following third attempt for Razor Shell was countered by Hydreigon's Double Hit, which was then followed by a Dragon Rush, finally defeating the Sea Otter Pokémon.
In There's a New Gym Leader in Town!, Oshawott volunteered himself to battle Cheren's Herdier. Oshawott's Hydro Pump attack was dodged easily by his opponent and his Tackle was overpowered by Take Down. Though Oshawott was able to block Herdier's Thunder Fang with Razor Shell, Cheren and Herdier were able to outsmart him and knock away his scalchop, distracting him before he was hit by a super effective Thunder Fang and got knocked out.
Oshawott came out of his Poké ball in Secrets From Out of the Fog! to help Pikachu and Axew convince the Pokémon at N's house to trust Ash and co. He later helped to battle Barret's Magnezone.
In Team Plasma and the Awakening Ceremony!, Oshawott was sent out alongside the rest of Ash's team to help Ash and N dig up to the surface of the White Ruins after they had fallen into a pit. While battling Team Plasma, Oshawott dealt massive damage to two controlled Golurk with his Hydro Pump attack. However, when Colress turned his mind control machine on them, Oshawott was quickly recalled to his Poké Ball along with Ash's other Pokémon, save for Pikachu.
In Crowning the Scalchop King!, Oshawott competed in the Scalchop King Competition on Scalchop Island. He had a rivalry with Caesar, a Dewott owned by Cadbury, as both fell in love with Osharina, who was the Scalchop Queen of the island. Both competitors made it to the final round of the tournament, where they battled against each other. After a long battle, Oshawott managed to defeat Caesar. Despite Oshawott's win, Osharina rejected him in favor of Caesar. Oshawott's scalchop broke soon after, disqualifying him from the tournament.
Oshawott was reunited with the entire Unova team at Professor Oak's Laboratory in The Dream Continues!. He joined the others in a group attack on Team Rocket with his Hydro Pump to send them blasting off for the last time in the Best Wishes series. Oshawott was left at the lab before Ash set off for the Kalos region.