This study aimed to examine the effect of incorporating the generative pre-trained AI chatbot, ChatGPT, into an instructor-led writing class on the motivation of Japanese university students. This study examines changes in students' Ideal L2 Self, Ought-to L2 Self, and L2 Learning Experience using Dörnyei's L2 Motivational Self System (L2MSS) framework. These changes were analyzed before and after students engaged with ChatGPT. A mixed-methods approach, including questionnaires and open-ended questions, was employed. Eighty students were divided into two groups: control and treatment. The treatment group participated in writing workshops, collaborated, and received feedback from ChatGPT. Students who utilized ChatGPT reported higher levels in all three motivational factors, although only Ideal L2 Self and L2 Learning Experience showed statistical significance. These findings highlight the potential of AI chatbots such as ChatGPT in enhancing motivation and writing skills. This research aims to inform instructional practices and pave the way for future advancements in AI-assisted language learning. By exploring the nuanced effects of AI tools on language learning motivation, this study contributes to the understanding of effective AI integration in language classrooms and offers valuable insights for educators and researchers.