Princess Dei is Genghis Rex's equally evil older sister and the only female Tyranno. She is a very skilled fighter with greater speed and agility than any other Tyranno and her physical strength also does not compare unfavorably with those of the others. She is also believed to be the co-leader of the Tyranno clan, ranking as high as her brother in the hierarchy and leading their forces on Reptilon, while Rex takes care of their business on Earth.
She is a Deinonychus, a vicious dinosaur of the Dromeosaur lineage with a razor-sharp toe claw that was used to cut and eviscerate prey or to slash prey with the intent of killing it through either shock or blood loss. Her kind existed at the Late Cretaceous, about 90 million years ago.
She is even more ruthless than her brother and will dare to scold him when his or her schemes go wrong. She appears considerably less than the other Tyrannos due to still being tied to her matters on Reptilon. She also offends the other Tyrannos, stating to her brother she does not understand why their ranks were chosen for such an important thing as the Tyranno Earth Mission.
Dei sees the Dinosaucers as pests who need to be eliminated and the only thing between the Tyrannos and their domination of both Reptilon and Earth. Like her younger sibling, she is seemingly unhindered by emotions or feelings and seems to care only for herself and her brother though she does appreciate the loyalty and respect of the other Tyrannos towards her.