Ukulele Pichu is an electric-type Pokémon distinguished by its permanent bond with a specialized ukulele. This instrument emits unique sounds when electrified, enabling Pichu to convey emotions and build connections with other Pokémon through music.

Originally inhabiting Dolce Island in the Oblivia region, Ukulele Pichu led wild Pokémon groups using its musical influence. Its peaceful life shattered when the criminal Pokémon Pinchers captured local Pokémon, including Pichu's companions. Witnessing this bred deep distrust of humans, prompting Pichu to attack the human protagonist Ben with Thunder Shock upon their first meeting, suspecting his association with the captors. After Ben subdued and calmed it, Pichu recognized his allyship and joined his missions to thwart the Pokémon Pinchers and rescue the captured Pokémon.

During a critical operation in Rasp Cavern, Ukulele Pichu confronted the Pokémon Pinchers alongside Ben. In a battle against the antagonist Red Eyes' Cranidos, the opposing Pokémon shattered Pichu's ukulele with Zen Headbutt, temporarily stripping Pichu of its expression and combat support. Ben later restored the instrument using special wood crafted by its original creator, Booker. Post-repair, Pichu formally solidified its partnership with Ben, remaining his steadfast companion in subsequent missions.

In combat, Ukulele Pichu employs a unique Pokémon Assist ability channeled through its ukulele. Activating it generates ascending musical notes that inflict minor damage on opponents and gradually fill a friendship gauge. After a brief duration, the ability culminates in a potent electrical shockwave. The Assist's effectiveness, duration, and power intensify as Ben's Capture Styler upgrades via accumulated Ranger Points. A specific limitation prevents Pichu from accompanying Ben during Celebi-facilitated time travel, requiring it to remain in the present era until Ben's return.