The Dark Demon World Arc (暗黒魔界編 Ankoku Makai Hen?) is the first arc in Dragon Ball Heroes. It was adapted into the Super Dragon Ball Heroes: Dark Demon World Mission! manga.
In the Dark Demon World, Trunks, Beat and Note confront Mira and the Masked Saiyan. Chronoa, Fen, Wairu, and Zen then appear. Chronoa signaled for them to attack the Masked Saiyan but the Masked Saiyan dodged and blocked most of their attacks but Zen managed to break a piece of the Masked Saiyan's mask. While the Saiyan was struggling, Mira shattered his armor and transformed into "Super Mira." Note, Trunks, and Beat were easily defeated by Mira and when Mira hit Beat with a kiai, Beat knocked into the Masked Saiyan and his mask fell off, revealing to be Barduck. Barduck then transformed into Super Saiyan 3.