Charon/Plot

Background
Charon was presumably made to keep tabs on Gieve they were also shown talking to someone else(presumably Lamia).

Additionally Charon has the ability to erase memories or at the very least Gieve's memory.

Fugitive Arc
Similar to Gieve, Charon first appears alongside him who were watching Jin and Tachikawa (with Izumi in the background) destroying Arugdas with only one strike for each trion soldier as commented by Gieve. In response to his comment Charon complimented the duo and asked Gieve if they were the trigger users from meeden Ergates was talking about beforehand then followed up with how they might get in the way of their mission to which Gieve responded with how they won't be a problem if that's all they got.