コエムシ, Dung Beetle

A weird creature who calls itself "Dung Beetle" (Coemushi) and becomes the children's tutor after Kokopelli's disappearance. It is able to communicate verbally, and is usually very sarcastic. It responds to the children's call, which includes Kana even though she didn't sign the contract. It is able to teleport the children, as well as others from the outside world to the cockpit, and vice-versa. However, it cannot teleport directly between two places, and must go through the cockpit beforehand. Between battles, it can be seen conversing with an unknown entity.

In the anime, is revealed that Coemushi was actually a human from another Earth who also participated in a series of battles to protect it. He tried to amuse their guide in order to become the successor, thus being able to survive, but in the end, another children was chosen. He then begged for a chance to survive and the guide decided to accept his request, by transforming him into his replacement. The person he is seen conversing with is actually her younger sister Machi, who decided to travel with him from world to world, helping to assemble people to sign the contract and fight for their world's sake, just like Zearth's group. However, while in the manga, Coemushi's attitude towards the children is mostly sarcastic, and sometimes, sadistic, in the anime he ends up being much more cruel, specially when he tries to convince Jun to let Kana sign the contract, but when Jun declines his request, he tries to make Kana sign the contract by force, and ends up being shot down to death by Machi using the gun Jun gave to her.

(Source: Wikipedia)