The Ctarl-Ctarl are a humanoid species in the Toward Stars Era.
Little is known of the Ctarl-Ctarl's history. They possess an interstellar empire that has warred with humanity in the past, although in the modern day, trade agreements have been established between them and cordial relations made. Most individuals seen in the anime show fear towards the Ctarl-Ctarl's reputation, and their race's physical prowess is legendary. The Ctarl-Ctarl are by the modern day accepted within human society, within reason, and can join in most human customs, such as the Heifong Space Race. One exception to this, however, would be their inability to participate in the Universal Strongman Tournament, due to a freak accident involving a Ctarl-Ctarl competitor becoming overly excited and biting off her opponent's ear, before being disqualified and going berserk, causing thousands of casualties.
The Ctarl-Ctarl boast an extreme degree of racial pride, considering themselves in the main to be powerful and strong. Their society seems to be based upon the general maxim of the strong crushing the weak, and regard shows of weakness with disdain. Equally, they regard failure with great severity. In many other regards, the Ctarl-Ctarl are noticeably human in their general behavior, able to be calm and composed, reasonable and respectful, and even gleefully happy at times.
The Ctarl-Ctarl are a metamorphic species, able to change their physical forms into that of more primordial creatures to enhance their strength and durability. This ability can be invoked to degrees, from subtle changes to full-on beast-mode. The ability to transform is dependent on a planets moon.
The resulting transformation is very powerful, but apparently takes a lot of energy to maintain, and so therefore is typically only used for a relatively short duration followed by an immense intake of food. The transformation is supposedly also affected by the phases of nearby celestial objects, but to what degrees and to what effects are never explained.
Aisha Clan-Clan refers to her own races' immortality, although it is denoted that the Ctarl-Ctarl can still be killed from exposure to the intense pressures and temperatures of space, as well as the destruction of the brain.
The race is also extremely durable. Aisha herself has easily shrugged off a hardened blade slash and no less breaking the blade while sustaining no damage to herself, a blast from a caster shell, although coming out dazed, submersion in active hot lava, feeling as if in a regular hot spring, and took beatings from three of the Anten Seven and while living to tell the tale.
Although not much is known about the culture of the Ctarl-Ctarl, some aspects of their lifestyle are hinted at or displayed throughout the anime. For example, Aisha cooks a dish known as "Gejidabo stew" - a foul-smelling, repulsive stew which is said to grant increased strength to both Ctarl-Ctarl and Terrans. They also appear to feature their own monotheistic religion, worshipping the "God of all Ctarl-Ctarl", as well as their own prayers, as exemplified when Aisha saw Duuz's body.