Oshawott first appeared in BW002 when Lexi met Professor Juniper. Oshawott was one of three Pokémon she could choose for her UnovaStarter Pokémon. Lexi immediately selected Oshawott, finding it's outgoing personality funny. She and Oshawott became good friends very quickly, and he was one of the most prominent members of her team. Along with Axew, it remained outside it's Pokéball for the whole time of Lexi's Unova journey, both times.
Oshawott struggled throughout his time on Lexi's team whether or not to evolve; and it was often a reason for his battle losses. Oshawott seemed to express desire to evolve at first, but after battling against a Dewott, he seemed intimidated and didn't like the idea of becoming larger and more mature. There had only been one instance where Oshawott nearly evolved - however, he tried his hardest not to and successfully halted his evolution. From that point on, he focused on making himself stronger, but only as an Oshawott, using his small size and biology to the best of his abilities.
In SI001 upon leaving Unova, Oshawott became sad and ran away from Lexi, scared and upset about leaving the region and all Lexi's friends. He was, however, retrieved and happily arrived at the Sinnoh Ranch with all of Lexi's other Pokémon.
He only made one other appearance from then on - when Lexi visited her sisters Ranch where all her Pokémon were now staying. Upon seeing each other, Oshawott embraced Lexi, showing their relationship was still strong despite not being together.
Oshawott is an attention-seeking yet loveable Pokémon; who loves to battle, play and socialize. He can sometimes be cocky when battling, although only against those it believes it can easily defeat, while often becoming intimidated by those who he believes he can't. He's boastful and proud-acting, liking to show off when his help is needed. He's hyperactive most of the time, which leads to him sometimes fumbling and causing accidents.
If things go wrong or he gets annoyed, he often throws his scalchop in frustration, although he immediately panics and picks it back up - happily smiling after retrieving it.