Gabwelius is a mysterious plush-toy-like lifeform that manifests before Akina Myodo. It initiates the Fated Clash, a battle royale where six chosen fighters possessing special cards called the "Six Desires" compete to have their wishes granted. Gabwelius provides Akina with the "Fated One of Miracles" card to enter this conflict. The character is linked to the phrase "Even though it's just a glimmer of hope, a miracle will descend upon those who reach out their hand," derived from its namesake card "Blest Dragon, Gabwelius" in the Cardfight!! Vanguard trading card game. Nao repeated this phrase to Akina during a childhood incident, though Akina initially failed to recall its origin.

After the Fated Clash concludes, Gabwelius reveals the tournament's true purpose and introduces Sybilt, an entity gathering holders of "Destined One" cards to commence the Destined Showdown—a subsequent conflict where participants similarly battle for wish fulfillment. Throughout this arc, Gabwelius remains present as the story explores the motivations and clashes between holders of Fated One and Destined One cards.

During the later DELUXE tournament arc, Gabwelius continues accompanying Akina as he searches for his personal reason to pursue Vanguard beyond his wish to heal his sister.