He acquired her in Hoenn during a festival that he always went to as a boy, but did not react in time and had a wish to get it. Later, however, Chimecho joined him and soon James caught her. She participated in one of Jessie's contests in Hoenn, but was knocked out by May's Combusken. After falling ill James left her with his grandparents to take care of for the time being and they gave him Mime Jr. as a replacement.
When Team Rocket saw a bunch of Chingling, they stole all three of them, but James went away with one of them, hoping to evolve it and live with his Chimecho at his grandparents' house. However, Chingling refused the offer, making James and Mime Jr. blast off in refusal.
Chimecho in James' memories
James holding Chimecho.
Chimecho in James's fantasy in The Bells Are Singing!