Dewott, as an Oshawott, was originally lived in solitude, where he would train diligently. When the group began swimming in the lake, Oshawott attacked them, believing them to be trespassing. He battled against Lewis' Aipom and put up a good fight before being defeated. After a baby Tympole was stolen by a poacher named Kai, Oshawott teamed up with Lewis to get it back. After Tympole was returned safely, Oshawott decided to leave his life of solitude and join up with Lewis, who caught him in a Poké Ball.
Oshawott participated in the battle against Team Plasma in Crisis in the Cold! He battled against a Team Plasma grunt's Purrloin and won.
In the following episode, Oshawott was used in Lewis' first Gym battle against Clay. He battled against Clay's Boldore and initially had some trouble dealing damage to the bulky Pokémon, while simultaneously taking severe damage from Boldore's powerful attacks. However, using its newly-revealed Focus Energy, Oshawott was able to power-up his moves and defeat Boldore with a powerful Shell Blade.
In Pokémon - The Musical!, Oshawott, along with the rest of the group's Pokémon, performed in a Pokémon Musical.
Oshawott was the first Pokémon used by Lewis in his Gym battle against Elesa in A Runway Gym Battle! It battled both of Elesa's Emolga, who constantly kept switching in and out of the battle via Volt Switch. Despite landing a hit on the male Emolga with Tackle, Oshawott was taken out by a super-effective Electro Ball.
In A Rivalry is Born!, Oshawott was used to battle Hugh's Pidove. Despite being at a disadvantage due to Pidove's ability to fly, Oshawott eventually managed to take it down with Water Gun. He then battled Hugh's Blitzle and lost.
Lewis used Oshawott as his third Pokémon in the battle against Burgh in The Art of Battle! He faced off against Burgh's final Pokémon; Leavanny. Oshwott was able to use his speed to disorientate Leavanny and hit it with Razor Shell. However, he was quickly defeated by Leavanny's Leaf Storm.
Oshawott was Lewis' second Pokémon in his battle against Cheren in Lewis Gets Schooled! He battled Cheren's Cinccino and, after a long battle, both Pokémon ended up knocking each other out, leaving Lewis with only one Pokémon remaining.
In Insult to Injury!, Oshwott was used in a Double Battle alongside Darumaka against Hugh's Snivy and Blitzle. Despite using a combination of Razor Shell and Gyro Ball, Oshawott was knocked out by Blitzle's Wild Charge.
Oshawott participated in the rematch against Cheren in Re-Class is in Session! He battled against Cheren's Watchog in Swadloon's place and managed to defeat it. Oshawott then battled Cheren's Stoutland, who used Sunny Day to reduce the power of Oshawott's Water-type moves. Due to this, Oshawott was easily defeated with Thunder Fang.
In Clowning Around!, Lewis used Oshawott to participate in a "balance battle" against a Harlequin and his Baltoy. Initially, Oshawott had trouble adapting to battling on the planks, but soon managed to get used to the experience. Oshawott was severely damaged by Baltoy's Ancient Power and evolved into Dewott as a result. Using its newly-learned Revenge, Dewott was able to reflect the damage he had taken onto Baltoy and defeated it with a well-timed Razor Shell.
In A Sky-High Battle Royale!, Dewott was used to battle against Skyla's Unfezant. Using Focus Energy to boost his power, Dewott was able to use the wind blowing through the Gym to his advantage and get up to Unfezant's level. He then landed on Unfezant's back and struck with Razor Shell, sending it back to the ground. Unfezant then used Air Slash to damage Dewott, but he countered with Revenge, defeating Unfezant. Dewott then battled Swanna and lost.
In Rise of a Legend!, while training with Nate's Turtwig, Dewott learnt Ice Beam. Dewott was later used as Lewis' third and final Pokémon in his Gym battle with Drayden. He battled Drayden's powerful Haxorus, who had already defeated Braviary. Dewott quickly became overwhelmed by Haxorus' sheer power, but soon managed to gain the upper hand by freezing the interior of the Gym, immobolising Haxorus. Using the now icy battlefield, Dewott was able to easily outmaneuver Haxorus and defeat it with Razor Shell.
Dewott was Lewis' final Pokémon in his Unova League battle with Benga in Benga's Last Stand! He was sent out to battle Benga's Dragonite and was able to land a super-effective Ice Beam. However, Dragonite quickly recovered and hit Dewott with Dragon Rush, dealing major damage to the Discipline Pokémon. Dragonite then attacked with Hyper Beam, which Dewott attempted to intercept with Water Gun. However, Dragonite's move proved to be far stronger and began to inch its way towards Dewott. After hearing Lewis' encouragement, Dewott learnt Hydro Pump, which was strong enough to push Hyper Beam back and hit Dragonite. Dewott took advantage of Dragonite's surprise and hit it with a powerful Ice Beam, defeating it and allowing Lewis to move on to the next round.
Dewott was Lewis' fifth Pokémon in his battle against Hugh in At the End of the Line! He battled against Chandelure and easily won. He then battled against Hugh's Gothitelle. After a long battle, both Pokémon ended up knocking each other out, leaving both Lewis and Hugh with one Pokémon each.
Dewott was Lewis' third Pokémon in his battle against Tunja in Turn Up the Heat! He battled against Tunja's Simipour and lost.
Lewis left Dewott at Professor Juniper's Laboratory when he decided to go to Sinnoh.
Oshawott, from his debut, proved himself to be a brave Pokémon, standing up for his friends without hesitation. He seems to follow the "act now, ask questions later" mindset, as he began attacking the group, thinking that they were trying to hurt his fellow Oshawott, without first clarifying if they were indeed a threat. His fearless nature also translates well onto the battlefield, with him being willing to fight any opponent he is put in front of, even if he has a type disadvantage. In Pokémon - The Musical!, Oshawott was shown to comfortable performing on stage.
After evolving into Dewott, he seemed to be more cautious. He remained extremely loyal to Lewis and hugged him after defeating Baltoy. He has become much more serious overall and is known to train himself even if Lewis is not present.