Originating as a simple clay figurine sculpted by Wataru Ikusabe for a school project, Ryujinmaru transforms from an inanimate object into a combat robot when infused with the spirit of the Gold Dragon, one of Shinbukai's Shinbu Dragon Gods, upon Wataru's arrival in the mystical realm and his first battle as a savior. It serves as Wataru's primary mashin throughout his journeys.
In *Mashin Eiyūden Wataru 2*, Ryujinmaru evolves significantly due to the power of Star Mountain and Wataru's courage, becoming "New Ryujinmaru" (新星龍神丸). This evolved form features a white color scheme and gains New Star Wings (新星翼), boosting all capabilities 1.25-fold and granting new powers like astral projection. Base status parameters are Power (60), Speed (70), IQ (70), ATK (70), DEF (50), and LUC (80) at Level 1.
Retaining core combat techniques such as Dragon Fang Fist (龍牙拳), Flame Dragon Fist (炎龍拳), and Flying Dragon Fist (飛龍拳), New Ryujinmaru phases out the Soaring Dragon Sword (登龍剣) and its elemental variants. New techniques include the Sky Dragon Fist (天空幻龍波), acquired after Wataru's growth in the third Star World, and the signature finisher Star Dragon Sword (星龍剣). Earlier techniques like the life-draining Blazing Dragon Sword (火炎登龍剣) are not retained due to their severe risks.
Ryujinmaru's true essence remains a mythological Chinese dragon with golden scales and elongated horns. This core spirit form is visible within the cosmic-themed cockpit during piloting, with Wataru operating the robot from the dragon's head. Communication is consistently candid and concise, primarily offering tactical advice during combat.
Beyond the main series, Ryujinmaru appears in the 2020 web animation *Mashin Hero Wataru: The Seven Spirits of Ryujinmaru*, where its essence fragments into seven spirits across different realms, requiring a quest for restoration. The *Never-Ending Tale of Time* OVA excludes mashin-based combat entirely, focusing on Wataru's quest without Ryujinmaru's physical presence.