Oshawott first appeared in Fussing and Fighting, as one of the Pokémon owned by Professor Juniper along with the other Unova starter Pokémon, Snivy and Tepig. After Tepig gets into a fight with Snivy, Oshawott unsuccessfully tries to get them to stop and constantly gets hit in the process. After being sent flying into a wall, Oshawott's anger reaches its boiling point and begins attacking Tepig and Snivy, forcing them to use any object in Professor Juniper's lab they could find to protect themselves. Eventually, Professor Juniper finds the three in their violent tussle and sends them back into their Poké Balls. The three sleep inside while Professor Juniper worriedly wonders if they are truly ready to be partners for the upcoming Trainers.
Later Oshawott, along with Tepig and Snivy, are sent to Black's home from the lab and the package soon reaches the boy's hands. Black's cold, which he got after staying in the rain while waiting for the package to come, causes him to sneeze and drop the box, releasing the Pokémon from their Poké Balls. Tepig and Snivy get into another fight which Oshawott once again tries to stop. Once again, Oshawott gets angry and violently attacks them. Tepig runs off and Black follows him, leaving Snivy at the mercy of Oshawott's rage. Later, Professor Juniper shockingly arrives to see the aftermath of the battle between Snivy and Oshawott. Next, Bianca and Cheren arrive wondering what had happened; while Professor Juniper worries about her broken Pokédexes, Bianca hands Cheren Snivy, stating that he resembled him, and takes Oshawott for herself.
In Welcome To Striaton City!!, after Bianca and Cheren arrive in Striaton City to tell Black to take care of his Pokédex, they get roped into his Gym battle. Oshawott, along with Snivy and Tepig, now named Tep, are used to battle the Gym Leaders, Cilan, Chili, and Cress. Before doing so, Oshawott is used to teach Bianca about Pokémon type compatibility by having Tep and Snivy attack him and teach Bianca which types are strong and weak against Water-type Pokémon. After passing through the Gym's challenge, they face the Gym Leaders. At first, Oshawott and the others are overpowered by the three Pokémon belonging to the Gym Leaders but eventually gain the upper hand when they use teamwork. Eventually, after blocking an attack by Cilan's Pansage, Oshawott retaliates by throwing its scalchop at Chili's Pansear, defeating it. Immediately after this, Oshawott has his scalchop shattered by Pansage and is defeated. Luckily, Tep managed to grab some of Pansage's leaves and feeds them to Oshawott and Snivy, rejuvenating them. Just as they are revived, the match's time limit ends, allowing Black, Cheren, and Bianca to win with 3-2.
In With a Little Help from My Friends, at Anville Town, Oshawott helps Bianca practice the flute by holding up sheet music for her to play. When Bianca meets with White, she reveals that her father had constantly been attempting to get her to return home. Due to her father's overprotective nature, Bianca was unable to train and become stronger, leaving Oshawott and Litwick unskilled in battling. Later, Oshawott was used alongside White's Amanda to battle a wild Vullaby at the Café Sonata to protect a wild Meloetta. Realizing that Vullaby's skull diaper was protecting a weak spot, White had Amanda distract Vullaby with Leaf Tornado, allowing Oshawott to throw its scalchop into the diaper undetected. This weakened Vullaby enough for Meloetta to defeat it, allowing White to catch and add it to her team.
After Bianca becomes Professor Juniper's assistant, Oshawott assists his Trainer with her work.
Oshawott is normally the calmer, shyer, and most peaceful of the three Unovastarter Pokémon that were supposed to go to Bianca, Black, and Cheren. However, whenever Oshawott loses his temper, he takes on another personality and goes into a violent frenzy. When angered, he will attack anything in the vicinity, usually destroying or harming whatever or whoever is unlucky enough to be near him.