Clem is the younger sister of Clemont, the Gym Leader of Lumiose City in the Kalos region. She travels alongside her brother, as well as Ash Ketchum and Serena, throughout the events of Pokémon the Series XY and XYZ. Unlike previous young companions such as Max, Clem is not a Pokémon Trainer herself, as she has not yet reached the required age. To allow her to experience the joy of caring for a Pokémon, her brother caught a Dedenne for her, which she keeps in her satchel and looks after as her own.

In terms of personality, Clem is portrayed as a remarkably firm and self-possessed young girl who acts with great determination. Her most defining trait is her boundless and unconditional love for all Pokémon. She shows no fear of any creature she encounters, finding something endearing in even the most intimidating or ferocious-looking species, much to the amusement of her friends. She is also notably brave and resourceful, often stepping up to help Pokémon in need. For example, when a Fletchinder was rejected from participating in an aerial competition for being too small, Clem advocated for it tenaciously, drawing on her own experience of being considered too young to fly, and her persistence was ultimately rewarded.

One of Clem's most persistent and humorous character traits is her self-appointed mission to find a suitable wife for her older brother, Clemont. She frequently and unabashedly proposes marriage to beautiful women on his behalf, often dragging him away by one of his mechanical Aipom Arms when he becomes too flustered. This behavior draws a direct parallel to Brock from earlier seasons of the anime. She also has a noticeable fondness for spooky stories and haunted houses, showing excitement rather than fear in such situations. In the Japanese version of the anime, Clem often refers to herself in the third person, a speech pattern that underscores her youth and childlike innocence.

Clem's role in the story is that of the group's youngest member and a source of emotional support and boundless positivity. She has a very close and caring relationship with her brother, who is highly protective of her, often worrying when she wanders off. She also grows close to Serena, who acts as an older sister figure to her, and she looks up to Ash with admiration. Throughout the XYZ season, Clem takes on a more significant role by befriending a mysterious Pokémon known as Squishy, which is later revealed to be a core of the Legendary Pokémon Zygarde. She cares for Squishy with the same dedication she shows Dedenne, and she makes a solemn promise to Zygarde that she will return for it once she officially becomes a Pokémon Trainer, demonstrating her sense of responsibility and deep empathy. This arc allows her character to show significant growth, moving from a simple tag-along to a proactive caretaker with a direct stake in saving the Kalos region from Team Flare. Her notable abilities include her persuasive determination and her skill in caring for and understanding the needs of various Pokémon, even without being their official Trainer.