Kolruu was someone Rahtinah knew in her youth, alongside another Yondard named Yonnie. Yonnie and Kolruu knew each other for longer, but they were all still good friends. However, an incident where Rahtinah wanted to get near a Shaft became a fatal incident, leaving them frying in the light. With her absorbtion powers, Rahtinah, regretfully, absorbed Yonnie when he begged her to do so, since both of them would otherwise die.

Kolruu managed to get to them, but with Yonnie gone, Kolruu blamed Rahtinah for Yonnie's death and broke off from her.

Kolruu would travel, but relatively quickly would find himself in a village full of various inventors, tinkerers, and others of the like. But due to issues, he would leave and would later reunite with Rahtinah. However, while he would, eventually, be on better terms with Rahtinah, he had his own issues to deal with, pertaining the the village he left, and his meeting of Fennia.

Kolruu is powerful, and is the second largest of the protagonists, but at a point seems to stick to a support position. He is also the only one who can effectively 'pilot' Fennia, their Autyon (Auto-Yondards, a sub species of Yondards that typically, but not always, largely lack their own sentience, and act as means of transportation for Yondards capable of controlling them)/ means of long distance travel.

While he keeps this to himself, Kolruu isn't a Yondard, per se. In fact he's closer to an Autyon himself. But he has his own secrets.