Having been captured early in his life for the purpose of study by humans, Glen carries a lot of trauma with him. Often controlled by magics he didn't have the strength to resist, he was used for a number of experiments, many of them painful - after all, his species had nearly committed genocide, what reason did the humans have to show mercy? Kept alive by Old World machines and magic alike, unable to die and return to the Core, he remained in captivity for many years. Left alone for long stretches, he eventually developed severe abandonment issues, to the point where he saw any attention, however painful, as better than nothing.
Finally, he was freed from his long imprisonment by another group of humans, who later told him they were both parties of a resistance but were factions at odds. Wary at first, he learned to trust over time, and his knowledge of the Old World picked up during captivity proved invaluable to this new group. In time, he learned the concept of family, and came to see these people as such. He didn't know where other kijikaiaku were, and didn't even know where to start looking.
He has served as guardian of this expanded family now for several of their generations, and until something pulls him away from them, he will continue to do so.
Quiet and reserved, he mostly keeps to himself. He's not the strongest kiji in the world, but he feels he doesn't need to be. So long as these mortals he's come to care for can enjoy good, long lives, he is content. Over time, he has developed a fondness for adopting other beings, often small animals, but arriving home with the occasional dragonling is also not unheard of for him. Like the humans who rescued him, he wishes to rescue others.