Kappe Alien (かっぺ星人, Kappe-Seijin) are a race of aliens that have taken refuge on the earth and therefore have become targets of a global alien extermination effort.
Gantz showed the hunters a target called the Kappe alien, but as before, the picture shown isn't always the boss.
The Kappe alien itself actually posed little danger during the mission. Rather, the threat lay with the "pets" of the Kappe alien, which were in turn a wide variety of aliens posing as dinosaur statues in a museum. Notable among them: three Triceratops with the ability to stand upright and increase their muscle mass, several Tyrannosaurus Rex could shoot fireballs from their mouths, and numerous raptor-shaped aliens with razor sharp tails.
The Kappe alien itself could increase in size and strength, but was eventually beaten by Kaze and killed by Izumi.