Sonansu is Jessie's Psychic-type Pokémon, notorious for emerging unsummoned from its Poké Ball—a habit that initially irritates teammates who eventually grow accustomed to it. It punctuates Team Rocket's exchanges with its signature utterance "Sonansu," cementing it as their verbal trademark. Typically appearing vacant and air-headed, it trails teammates blindly yet sporadically reveals sharp battle intellect. Despite its dopey exterior, Sonansu exhibits fierce loyalty to Jessie and the team, displaying deep affection toward them. It willingly accompanies members like Meowth on side missions.

This Pokémon also pursues romantic interests, developing attachments to a kind Kirlia and later Dr. White's Wobbuffet. Though it briefly stayed with its mate, loyalty drew it back to Jessie; during a critical moment, it shielded the team using Counter. In combat, Sonansu employs purely defensive tactics, wielding Counter and Mirror Coat to rebound foes' assaults. Its effectiveness hinges on precise timing, transforming it into a strategic shield. Outside battle, it applies learned skills—crafting Poké Puffs for performances and joining disguise operations, sometimes masquerading as human alongside teammates.

During the "Pikachu to Eevee Friends" event, Sonansu aided Meowth in preparing food for Eeveelutions. Blasted away by Umbreon due to a misunderstanding, it returned to misinterpret a peaceful gathering as conflict and attacked—prompting Sylveon to repel it again. Its persistent attempts to rejoin the group underscore its loyalty amid recurring mishaps. Temporarily reverted to Wynaut after spacetime disruptions, it regained its form once distortions ceased. As one of the series' longest-serving Pokémon, Sonansu consistently appears alongside Team Rocket across regions and arcs.