[spoilers below, don't read if you haven't recruited Hydel yet!]
Hydel is the second general of the Four Generals of the Black Swarm the player meets. He is chiefly concerned with justice, despite piloting a cockroach, wearing what he is wearing, and fighting for all he's got as a member of the Black Swarm. His subordinates were Akane and Minoru, and he continues to act as a guardian to Minoru after he joins the group. He greatly respects humans as a whole, and respects the right for them to make decisions and have morals of their own, as long as they believe it is the right thing to do. He lets Minoru and Akane join who he percieves as the badguys, and shows fair game and outrightly waits for the group to get to the third Origin until he runs for it.
He doesn't hate nor prefer cockroaches, and probably thinks they're somewhat offensive, but he doesn't judge them, he says he merely chose his drone because he admired its fighting style the best. This speaks volumes to his character, and his integrity in being fair, honest, and willful for riteousness. Although he is very strange, he is also a very relatable person. If not for his penchant for hiding behind doors, constantly speaking about justice, and piloting a cockroach that flies, he acts and speaks completely normal.
He is the most prominent character of the four generals, and is in fact involved almost as the player's viewpoint from inside Dr. Gidoh's base until he leaves, is the sole reason Dr. Gidoh doesn't have the third Origin and Dr. Sakuma does, narrates the change to apocalyptic Cimexus, sets the tides of the generals joining the group, returns Shoya and Yui back to the group, and tell the player the biggest story chapter secret.
His drone is a cockroach named Jet-I. This is a not-so-subtle reference to Star Wars, and also a reference to how strange he is, how fast his drone is, presumably with the help of rocket jets, as well as his method of propelling his melee attacks. Although his drone can technically fly with these jets, there is no feature for his drone to jump over units or water.