Rockruff is either the offspring of Ethan's Lycanroc, or was found and caught by Ethan near Clawmark Hill to later give to a young Riley. The answer is unknown.
Rockruff makes her debut in the Prologue/Episode 1, where she is sitting next to Riley getting ready to begin their journey together. Rockruff was given to Riley was a gift from her brother, Ethan Sterling before he went missing.
Personality and characteristics
Much like her species, Rockruff is a playful and affectionate Pokémon that gets along with many people, including Riley. Rockruff is very protective over Riley and takes it very seriously. She vowed after being given to Riley to always protect her.