Aaron

Aaron (アーロン) is a Intelligence Support Activity member of the United States Special Forces who frequently worked with Mia Cyrus.

Personality
Like his Japanese counterpart Iizuka, Aaron is a no-nonsense individual who is deeply involved with military affairs.

Just Cause Mia
Aaron and Mia didn't interact much, but it is likely that Aaron at least somewhat had interactions offscreen.

Shantoulon Peipei and Astrologer
As Peipei's American liason, it is likely that Aaron had a relationship with her and Astrologer.

Julia
Since Aaron is rarely seen without Julia, it is inferred that the two have a close relationship.

Babel Brigade Arc
Aaron, along with Julia, accompanies Mia to Tijuana, Mexico and Japan, where they discover the Greenburg twins in magical cubes.

Ukraine Arc
Aaron is seen at the end of the arc when the American military offers Lau Peipei and Astrologer housing and a liason.

Trivia

 * Aaron was voiced by Takahiro Shimada in Japanese and Christopher Wehkamp in the English dub.