Guchi is the longtime pet of the main character On-chan, having been with him since their time together on the Parade Planet, their home world. Guchi is a creature characterized by a slender body, a light orange color, and typically moves on all fours. One of Guchi's most notable and unique abilities is the power to change size, a trait that sets this companion apart from other characters.

In terms of personality, Guchi is defined by a gluttonous nature and a clumsy disposition. However, this character possesses an inherent positivity that allows for a quick recovery from feelings of sadness or discouragement. This optimistic outlook ensures that Guchi remains a cheerful presence even when faced with challenges or minor failures.

Within the story, Guchi’s primary role is as a faithful companion to On-chan, frequently accompanying him during explorations of their town. Through these everyday adventures, Guchi engages in shared activities and learning experiences with On-chan. The character also interacts with the wider recurring cast, including On-chan’s childhood friend and girlfriend OK-chan, as well as On-chan's rival No-chan, often taking part in playful or mildly challenging scenarios. These interactions help to depict a sense of communal life and shared experience among the group.

Regarding character development, official descriptions present Guchi consistently as an integral part of On-chan's world without significant alterations to background or core characteristics. This stability is observed across the character’s various appearances, including the feature film On-chan's Dream Power Adventure! from 2003 and the television series Yumemiru, Anime on-chan from 2008. Guchi’s presence consistently contributes to the gentle, positive atmosphere of On-chan's daily explorations and adventures.