Teru Yumemi, a shy third-grade student and the story's main protagonist, lives with his older sister Cocoro Yumemi, mother Youka, and father Dai. Initially overshadowed by Cocoro's dueling prowess after suffering numerous defeats to her, Teru also loses a duel to classmate Chishio on his first day of school, highlighting his early confidence struggles. His journey commences when he and Cocoro encounter Rei Kukami, fleeing pursuit by the organization Nest. Rei belongs to a family sworn to protect the ARC pendant, which safeguards the Great Spirit of Duel Masters. After Teru aids Rei, she introduces him to her grandfather, Kenshiro Kukami, who operates a dojo dedicated to teaching Duel Masters. Seeking strength to protect his friends and emerge from his sister's shadow, Teru joins the dojo.

Teru wields a Fire and Nature civilization deck, mirroring his idol Shobu Kirifuda. His deck aligns with the DMC-32 Mars Flash and DMC-33 Edge of Dragon products, featuring Supernova Mars Disaster as his strongest card. During a bravery test, he wins another powerful card, Supernova Ixion Burning Rave, though he refrains from using it in later duels. He entrusts this card to Rei for her collection of conquest cards tied to the ARC pendant's mysteries. Rei eventually returns it, instructing him to use it only when lacking other strong options. Teru duels in a technologically advanced setting where physical cards are replaced by a deck holder and virtual headset, enabling immersive gameplay through gestures and voice commands; this system also functions as a communication device.

Teru develops rivalries, notably with Hayate, who shares his goal of protecting the ARC pendant. Through relentless duels and training, Teru grows stronger, aiding Rei against Nest. The conflict escalates when Nest member Chikage Kasumi seizes control of the pendant and a Guardian Card. Although Teru possesses a Guardian Card, he is not yet the chosen one. To earn the legendary duelist title, he duels Hayate—another Guardian Card holder—and wins, gaining Hayate's acknowledgment. Teru then defeats Chikage, securing all Guardian Cards and dismantling Nest. These victories cement his status as the era's legendary duelist, capable of protecting the Great Spirit within the ARC pendant. The Guardian Cards represent evolved versions of earlier Awakening Cards, reflecting the altered timeline and new guardians of the creature world.