Bonnie.

Bonnie is Clemont's much-younger sister, roughly eight years old when XY opens. Too young to legally own her own Pokémon, she carries her brother's Dedenne in a special shoulder bag and operates as the cast's heart-of-the-group point-of-entry character. Running joke: she asks every adult woman the group meets to consider marrying her brother Clemont (the show plays it as innocent matchmaking; the writers gave it diminishing returns by XYZ but never quite dropped it).

The Zygarde Core / Squishy bond is the show's most plot-significant Bonnie arc. She finds the green blob of a Zygarde Core in XY074; befriends it; later realizes (in the back half of XYZ) that Squishy was a fragment of Zygarde 10% Forme. The bond becomes the linchpin of the Team Flare climax: Bonnie's presence stabilizes Zygarde's full transformation, and her tearful goodbye in XY127 was one of the most-cited emotional beats of the era. Returns to Lumiose with Clemont in XY141.