Grieffas Kredo commands the Dracter alien forces invading Earth under Queen Crouzade Laia. His calm, level-headed demeanor secures the queen's absolute confidence. Exploiting a period of the queen's instability or madness following the invasion, Grieffas seizes power in a coup, declaring himself the new emperor of the Dracter race. His ascension specifically targets Princess Arshem Laia, the queen's daughter and advocate for human coexistence.

Grieffas pilots the unique Dark Knight mecha, equipped with a force field-generating mechanism that drastically reduces incoming damage in combat, underscoring his strategic military position. Salvaged components from an abandoned Dark Knight unit are later recovered by the human Victor and repurposed to construct the Megaton-Class Rogue mecha piloted by Princess Arshem.