Castro is a human command division officer on the USS Cerritos, first seen as an ambitious ensign among the self-styled Redshirts and later listed as a lieutenant junior grade.
Castro is a human Starfleet officer serving in the command division aboard the California-class USS Cerritos under Captain Carol Freeman in the early 2380s.
In The Spy Humongous, Castro is one of the Redshirts, a clique of command ensigns led by Casey who practise speeches and poses in the hope of fast promotion. When Brad Boimler joins the group, Castro invites him along to one of Winger Bingston Jr.'s one-man shows. The Redshirts' posturing proves useless during a crisis, and Boimler walks away from them.
Castro remains part of the ship's company in later seasons of Star Trek: Lower Decks, by which time the character holds the rank of lieutenant junior grade.