Oshawott is a happy and energetic Pokémon who wants more attention from people, and he even pushed Pikachu down from Ash's shoulder when he first began his journey. Unfortunately, this causes him to break up the friendship with the two other Unova starters, Snivy and Pignite and develop a rivalry with him instead at times. In addition, Oshawott is a very immature romanticist and gets lovestruck easily, though he always ends up being rejected by female Pokémon. After he was rejected by Osharina the female Oshawott, his "love-disease" is worsened. However, he really treasures his Scalchop, and he becomes unhappy and uncomfortable when he loses it or breaks it.
When Dawn was introduced to the group, Oshawott has a strong rivalry with Dawn's Piplup as both are Water-type Starter Pokémon who are competing and fighting each other because both had a huge crush on the Mythical Pokémon Meloetta upon her introduction. However, when Meloetta leaves with Ridley, Oshawott was seen emotionally crying in depression just like Piplup did before him when Dawn says goodbye to Ash and the group.
Oshawott was one of the Unova Region's starter Pokémon who was under the care of Professor Juniper. When the new Trainer, Trip, and Ash who had arrived from Kanto before Trip got here in Nuvema Town witnessed the three Pokémon being shown for the first time, Oshawott made such a good impression that Ash even called him "cute", causing Oshawott to become embarrassed.
Trip chose Snivy which caused Oshawott to become as still as a statue and fall over in shock. Oshawott, however developed an interest in Ash and left Juniper's lab, following the young Trainer from a distance. Oshawott later proved his worth by saving Ash's Pikachu and Iris' Axew from Team Rocket's clutches before fleeing the scene.
Oshawott finally showed himself to Ash and begged for Ash to take him along. Unfortunately, after attempting to capture Oshawott in a Poké Ball and failing, Ash realized that the Oshawott in question was the same one he had seen back at Professor Juniper's lab. Ash contacted Juniper who had become worried over Oshawott's mysterious disappearance and after getting her approval, obtained Oshawott's Poké Ball which gave Oshawott permission to fulfill his dream of travelling with Ash at last but Oshawott had gone missing again. After nearly falling into boiling water while stopping a dam from cracking, Ash saved Oshawott's life by returning the Pokémon to his Poké Ball, resulting in Oshawott becoming Ash's newest addition to his Unova team and also a permanent member of his overall team of Pokémon.
In The Battle Club and Tepig's Choice!, Oshawott came out of his Poké Ball two times when there's a battle going on and wants to fight but can't even fight a Dewott, and he wants to help out Pikachu catch the mystery Pokémon but fails when he's eating the bait they've set up.
In Triple Leaders, Team Threats! Oshawott was sent out on the last gym battle against Cilan's Pansage but he gets scared at first when he's at a disadvantage and hides behind Ash. Which actually got Ash and Pikachu annoyed as they push him onto the field. Ash told Oshawott about the great things he did so far even Pikachu and Axew were in trouble. So Oshawott is ready to fight which it didn't go well after all as Pansage uses Solar Beam. In Dreams by the Yard Full! Oshawott actually deflects it with his scalchop when Ash told him before it hits. He also use his scalchop as a shield to block Bullet Seed multiple times and quickly lost its scalchop in mid-air while using Razor Shell when Cilan's Pansage used Bullet Seed. Ash came up with an idea as he told Oshawott to use Water Gun towards the wall so it would bounce off the wall and the rocks like a pinball to shoot the scalchop off the ground and into the air so he would be able to grab it and finishes off with Razor Shell to win.
Oshawott also seen as an aquaphobic when he closes his eyes during his execution of using his Aqua Jet until he overcomes his fear by beating a wild Palpitoad with this ability before Ash captures it. Oshawott also gets the weed to cure all of their Pokémon's poison status.
During his battle against Stephan's Blitzle, it manages to loses his scalchop much to Oshawott's discomfort. He is also trained using a large scalchop crafted by Cilan's Dwebble in order to fight Stephan. Once the large scalchop breaks, Oshawott manage to defeat it due to his powerful speed as Iris' Axew recovers his scalchop back much to his excitement.
When Meloetta was introduced in All For The Love of Meloetta!, Oshawott gains a crush on the mythical Pokémon until the arrival of Dawn and her Piplup. Throughout the episodes, Oshawott gains a strong rivalry towards Dawn's Piplup due to their crush on Meloetta until Dawn's departure after the Junior league.
After Team Rocket's Operation Tempest is thwarted by Ash and the group in Unova's Survival Crisis!, Oshawott emotionally cries in depression when Meloetta is about to leave with Ridley and his Golurk when she finally say goodbye to Ash while Ash's Pikachu tried to calm Oshawott down when he is still crying emotionally.
In Cameron's Secret Weapon!, Oshawott was used in the Unova League against Cameron's Hydreigon. Despite the notable size difference and ineffective moves, Oshawott was a reasonable opponent for the brutal Pokémon, and hit him right away 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 fires a Tri Attack, which Oshawott was unable to block, taking more damage. Oshawott fights 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 Oshawott.
After Ash loses to Cameron in the Unova league, they travel through the Decolore Islands and upon arriving at the Scalchop Island, Oshawott develops a rivalry towards Caesar for the love of Osharina the female Oshawott and its queen and both competed at the competition and Oshawott wins the duel but got rejected by Osharina despite winning the competition for Ash. Worse than that, he got disqualified because of his Scalchop was broken due to being heartbroken leaving Caesar as the winner and also revealed that Osharina likes Caesar instead of Ash's Oshawott whom she strongly dislikes him.
Back on the ship, Oshawott is still saddened for being rejected and his scalchop has bandages knowing it was broken due to his broken heart. Nonetheless, he fell in love again when he saw a female Cinccino on the ship and tried to impress her, making Cinccino frightened and annoyed.
- Oshawott is the first of all Ash's starters to not be caught after a Grass-type starter was captured (Tepig was second as always with fire types), Ash captured a grass-starter in each region first, then catching the other starters later on.
- Besides Pikachu and Froakie, Oshawott is the only other starter Ash got from a professor.
- Ironically, Oshawott and Froakie are the Water starters of their regions, which is what Ash wanted to start his journey with when he planned to pick Squirtle as his starter.
- Oshawott knows how to come out of his Poké Ball on his own much like Misty's Psyduck, Brock's Croagunk, Jessie's Wobbuffet, May's Skitty and Munchlax. However, like Psyduck, Oshawott is a Water-type Pokémon.
- A running gag is when Oshawott is not chosen for battle, he becomes a white statue and faints.
- Oshawott's water-related fear is similar to Misty's Psyduck's Hydrophobia when he closed his eyes underwater and even using Aqua Jet. However, Ash helped Oshawott overcome this fear in the episode Facing Fear with Eyes Wide Open!
- When Oshawott is mad, he throws his scalchop on the ground, picks it up, and places it back on his chest.
- Sometimes, however, he throws it too far, and runs after it before it gets lost.
- Oshawott can sometimes be jealous of Ash's and Pikachu's relationship (similar to Bayleef and Aipom). However, it was only shown in the first few episodes of Pokémon: Black & White.
- Oshawott is one of the few of Ash's Pokémon to develop romantic interest for other Pokémon. The others are Butterfree, Bulbasaur, Charizard, Totodile, Corphish and Sceptile.
- Oshawott seems to be Brock's replacement as the flirt, being the more romantic member of Ash's team, as he's developed more crushes on any other Pokémon than anyone else on Ash's teams in the entire anime:
At Oak's Lab
At Kukui's house
At Cerise Laboratory