Guchi is On-chan's longtime pet, possessing the unique ability to change size. Exhibiting a gluttonous nature and clumsy personality, Guchi's inherent positivity allows quick recovery from sadness or discouragement. The character frequently accompanies On-chan during explorations of their town, engaging in shared activities and learning. Guchi interacts with other recurring figures, including On-chan's childhood friend and girlfriend OK-chan, and On-chan's rival No-chan, within various playful or challenging scenarios. Guchi's presence contributes to depictions of everyday adventures and communal life involving On-chan and townspeople. Official descriptions consistently present Guchi as a companion integral to On-chan's experiences, without significant alteration or development in background or core characteristics across different appearances, including the feature film "On-chan's Dream Power Adventure!" (2003) and the television series "Yumemiru, Anime on-chan" (2008).