Dan Yamada, operating under the alias "Da★Dan," emerges as a minor antagonist. He initially disguises himself with a mask mimicking protagonist Yuga Mikado to frame Yuga for destructive pranks and tarnish rival PalTubers' reputations. His core drive is amassing online infamy and viewership through malicious schemes, such as hijacking the RanGa Channel to broadcast humiliating footage of Yuga's Buddyfights and targeting supporter Miko Mikono after she endorsed a competing channel.

Initially acting alone, Dan later aligns with primary antagonist group Lost World, specifically begging Vile Ranma for power. He receives a "lostrizer" card, corrupting his primary Buddy †Dragonblood Eyes† Bloody-Eyes into †Huskblood Eyes† Deadly Eyes. Dan's deck leverages the 《Dragonblood Sect》, focusing on counterattacks that punish opponents for targeting Bloody-Eyes to inflict damage and gain advantages.

Despite this enhanced power and wagering all his points in a high-stakes duel against Yuga, Dan loses when Yuga activates Gargantua Dragon's "Gatling Mode." Post-defeat, Dan joins the Vile Ranma Channel, producing promotional content and executing missions for Lost World, including scouting Eden Hanazono for recruitment.

His downfall follows manipulation by antagonist Seiji, provoking Dan to rebel against Vile Ranma. Though Dan destroys Vanity Husk Destroyer in their clash, Vile Ranma summons the monster's evolved form. Intending banishment, Vile Ranma instead watches as the creature devours Dan, seemingly killing him. This event later materializes in Seiji's nightmare as a zombie-like Dan Yamada, clutching a bloodied championship trophy and blaming Seiji for his death.

However, Dan physically resurfaces unharmed when Destroyer coughs up a cocoon that releases him, appearing unscathed and possibly asleep during his internment. He flees in panic upon encountering Destroyer again. His Buddyfight record details consistent losses to Yuga (multiple times), Miko Mikono, Eden Hanazono, Vile Ranma, and Mel Yumegatari.