Guan Yu (Kan U) Gundam stands among the three sworn brothers alongside Liu Bei (Ryuubi Gundam) and Zhang Fei (Chouhi Gundam), their unbreakable bond driving their shared destiny. Pursued by Dong Zhuo (Toutaku Zaku)'s forces, the brothers confront Toutaku's troops on a cliff. Koshin Gyan, a general serving Toutaku, taunts them and springs a trap, destroying a bridge and sending the brothers plummeting into the river below.

Rescued by Ma Chao (Bachou Blue Destiny), Guan Yu fights in subsequent battles against Koshin's incursions. When Liu Bei discovers the loss of the Ryuuteiken sword, the brothers press their assault regardless. Ma Chao retrieves the sword after encountering a dragon spirit in the river, returning it to Liu Bei mid-conflict.

Empowered by the sword's return and bolstered by Ma Chao and villagers, Guan Yu, Liu Bei, and Zhang Fei unleash their combined technique, the "Holy Trinity," decisively overwhelming Koshin Gyan.

Beyond these events, Guan Yu achieves an evolved combat form: Wu Sheng Guan Yu ν Gundam. This form signifies combat mastery, wielding an enlarged, enhanced weapon—the Seiryuengetsuto—extending his reach and cutting power against foes. Throughout, Guan Yu exemplifies unwavering loyalty and combat prowess within the sworn brotherhood.