Nessa was born and raised in Galar alongside her brother Marlon, whom she knew as her best friend. They are apart of a family of anti-royalists who for generations and generations have been advocates for free-will and peace without a monarchy at the helm, although the family admits the reasons for this have faded over time. She loved her hometown and was known as the most popular girl in town. When her brother left to go travelling, she started an intense training regime to become stronger while also aspiring to become a model. Her father is a fisher, and her mother works in the marketplace, which is what influenced her into becoming a Water specialist. She met Sonia during their Gym Challenge, and they continue to be close friends, with Nessa often giving Sonia fresh seafood from Hulbury whenever they meet up. Nessa is incredibly popular, both as a Gym Leader and as a model, and often she is recognised by fans while travelling. She is also close friends with Elesa due to their modelling careers.
Nessa is first seen in the series in A Deep Thought! when Marlon introduces her and his "model" sister. She appears very cold to many, yet feisty and flirtatious with Calem. She seems very in tune with her ancestory, being the one to speak about her families ties to the Darkest Day when Marlon reveals Lexi's chance meeting with a mysterious Pokémon. She joins the group when a distress signal is called at the Hulbury lighthouse which results in her helping the team restore the cities power when a Barraskewda becomes tangled in the underwater wiring of the cities power bank. In this time, she is impressed with her brothers friends tenacity to help people, and warms up considerably to them following this. She next appears when she is revealed to be the Hulbury Gym Leader, something even Marlon was unaware of. She then faces Lexi, and Calem in a Gym Battle, which she awards all three Gym Badges. After Lexi has dinner with Chairman Rose (someone that Nessa is very suspicious of) she decides to accompany the team on their journey, revealing that she doesn't trust the fate of their family in her brothers hands alone.
Her journey with the team was in a supporting capacity; she revealed to Lexi that living in Galar and particularly Hulbury is all she's ever known (apart from one holiday that she doesn't remember), but also admits that its what has held her back in both her careers. Being a model, she revealed she is unable to excel in it due to her inability to travel due to being a Gym Leader, but refuses to give it up with her aspirations to also become Champion. Her dream is to become the most popular model & Champion in the world; however she admits that her training has been taking a back seat ever since finding out about Lexi's meeting with a mysterious Pokémon & its potential ties to Sonia's research, of which Nessa is very keen to discover due to its potential ties to her families origin. Nessa often is quiet and reserved yet scolds her brother on any opportunity she can. She is very wise and knowledgable and often is Lexi's "wingman" in battles with her support. She uses her own Pokémon sparingly, hardly utilising them throughout her time with the team.
As time progressed, Nessa learn to open up more to the team. She revealed that her time away from the Gym allowed her to see her future as potentially not what she's set herself on, questioning whether or not she is able to continue with her aspirations. Her relationship with Chairman Rose is frosty due to his often mocking remarks at these aspirations, with him telling her the reason she fails to progress is due to her lack of focus. She is also very wary of him due to his goals for Galar, which Nessa sees as opportunistic for him to heighten his status in the region.
As Sonia pieces together the story behind Zacian and Zamazenta and the Darkest Day, Nessa and Marlon uncovered the secrets behind their family origins, discovering that their ancestors opposed the royal families decision to cover up the Pokémons history with Eternatus, instead replacing this with the first kings ancestor as the hero. They also discovered that they themselves were the creators of the Rusted Sword and Rusted Sheilds that were the sources of the Legendary Pokémon's powers. With the truth revealed, Nessa realised that she could once again focus on her goals, which led her to compete in the Champion Cup, and upon battling up the ranks which included defeating Calem, she became Champion, having beat Leon in the finale match. Upon gaining the title, she decided to leave the group in order to take on her role seriously, alongside hoping the new status would help her modelling career in the future.