Thearen (aka Night Stealer) is a guild agent in the Mishion guild before Anthony Irin joined the guild. Anthony mentions that Thearen came and spoke at Anthony’s school, and because of that, he joined the guild. Thearen first shows up in the story Dark Band Risen, in which he goes by the name Night Stealer and attempts to kill Anthony. Thearen explains (and the guild chief later confirms the story) that he heard reports of missing guild members and decided to investigate. When he found out that the old guild chief was creating mutated lifeforms out of guild agents he found troublesome and selling them to corporations on Earth, he attempted to expose the guild chief. The old guild chief made it look like Thearen died from an electrical shock, but actually created a mutated life form out of him by DNA manipulation.
Thearen later escaped as a damaged, barely living goblin creature. The Dark Band took him in and named him Night Stealer. He worked with them for several years, plotting Cypostello’s downfall. By the time Anthony Irin was rising through the guild’s ranks, Night Stealer had cultivated a hate for the guild that had betrayed him.
Anthony managed to turn Night Stealer back to the guild’s side at the end of Dark Band Risen, and it was Night Stealer who saved Cypostello and stopped Death Grim. Thearen underwent treatment for his ailments and soon started work as a guild agent once more. While he never regained his full six feet (now a three-foot midgit), he returned to normal otherwise. He is one of the most important members of Anthony’s team and a loyal friend.
Overall, Thearen contributed in some of the biggest ways to the Mishion Guild, saving it and preserving it.