A boy who was raised in the Sidonia's underworld, he had troubles adapting after returning to the upper levels. Is a compulsive eater with a large appetite.

The first Sidionian who Tanikaze became friends with. She is also his classmate and fellow squadron team mate and 2nd ranked Guardian pilot among the trainees.

A Guardian pilot who quickly becomes Nagate's best friend, constantly accompanying Nagate and teaching him about the life inside Sidonia. Izana is a new third gender of humans who are asexual, yet can change their gender to either male or female depending on the other party.

A fellow male Guardian pilot with long white hair, heir of Kunato Industries, the company developing the Type 18 Guardians. Norio ranked first during pilot training and had little respect for other trainees, developing a rivalry with Nagate given the special treatment he receives. His body is later taken over by Ochiai's mind.

A friend of Nagate and Izana. She later develops feelings for Nagate and competes with Izana for his attention. She is later promoted to Assistant Commander in Guardian Operation on board Sidonia and moves to Nagate's house as well.