Clefable, as a Cleffa is Ui's first Pokémon she caught after being mentioned by Yui during the reunion.
Ui made her official appearance alongside Jun in Sewing With Mio!, after seeing Yui return with her newly evolved Goodra. She had a Pokemon of her own which was a Pokemon egg which later hatched into a Cleffa, she is a female Cleffa who shares Ui's personality.
She and Yui's Goodra was attacked by Team Rocket, Jessie's Gourgeist and James's Inkay attacked Yui and Ui, Cleffa got hit instead by shielding them and enduring the attacks resulted Cleffa to evolve into Clefairy thanks to Ui's heartfelt call and learned Meteor Mash and Moonblast which made Team Rocket blast off.
After spending a long time as a Clefairy, she finally evolves into Clefable after finding Yui's Moon Stone that she was hiding behind Geeta in Jumping Over The Moon Stone!. Despite her evolution, she is really the big sister type, and somewhat motherly-like due to its personality.
In "What's In a Nickname?", she was officially nicknamed Bella by Ui, and even nicknamed the other Pokemon she has owned.
Clefairy's known moves are: Moonblast, Metronome, Flamethrower, Meteor Mash, and her ability is Cute Charm.