Mallow is a student at the Pokémon School on Melemele Island in the Alola region. She has a slender build with tan skin, long green hair styled into two tree-shaped twintails, and light green eyes. She is often seen wearing a pink and gray outfit with a flower accessory in her hair, which is held in place by vine-like straps.

Mallow is an energetic and friendly person. She was quick to welcome Ash Ketchum when he first arrived at the school and makes an effort to make others feel at ease. She can sometimes be overly enthusiastic, causing her to overlook minor details or jump to conclusions, but her optimism and warmth are consistent traits.

Her primary motivation is to become a skilled cook and help her family. She works at the Aina Cafeteria, which is run by her father and brother in Konikoni City. Her long-term goal is to make the Aina Cafeteria the best restaurant in all of Alola, and she regularly experiments with new recipes and hosts taste-testing sessions for her classmates.

In the story, Mallow is one of Ash’s closest school companions and a core member of the group of students who train and go on adventures together. She participates in many school activities, field trips, and challenges, including the island trials and the Alola Pokémon League. She also becomes a member of the Ultra Guardians, a group formed to capture Ultra Beasts that appear in the region.

Mallow shares a particularly close bond with Lana, who has been her childhood friend since they were very young. The two often joke around and support each other, and they eventually face off in a friendly but full-power battle during the Alola League. Mallow is also a supportive friend to Lillie, helping her overcome her fear of Pokémon and encouraging her growth throughout the series. She gets along well with all the other members of the school group, including Kiawe, Sophocles, and of course Ash.

Over the course of the series, Mallow experiences significant emotional development. It is revealed that her mother passed away from an illness when Mallow was young. In an episode set on Poni Island, the mist produced by the guardian Tapu Fini causes Mallow to see a vision of her deceased mother. This allows her to finally express the feelings she had held inside for years, including the regret she felt over a harsh comment she made as a child. After this emotional reconciliation, a Shaymin appears, and Mallow takes care of it until it is able to rejoin its friends. This event deepens her emotional maturity and reinforces her connection to themes of family and gratitude.

Mallow focuses on Grass-type Pokémon. Her primary partner is a Bounsweet that was originally caught by her mother as a gift. This Bounsweet later evolves into a Steenee during a battle with Team Rocket, and eventually into a Tsareena after a PokéDance competition. Tsareena knows moves such as Trop Kick, Magical Leaf, and Sweet Scent. Mallow also temporarily cares for a Shaymin, which she does not officially catch but looks after until it transforms into its Sky Forme and departs. She is noted as the only main character in her series who was never seen catching a Pokémon of her own on screen. In battle, Mallow and her Pokémon work well together, using the power of Z-Moves, including Bloom Shine Extra.