Onyango is a veteran fire soldier and a Third Generation pyrokinetic who holds the rank of lieutenant in Special Fire Force Company 1. He is an elderly man, notably shorter than many of his younger colleagues, with a bald head and metallic pieces attached to his temples. Thin metal cords extend from these pieces and stop around his jawline. His time away from active service left him somewhat less physically fit than he once was, and his age is a visible part of his character.

Onyango had previously retired from the Special Fire Force, but he returned from retirement after the death of Rekka Hoshimiya, stepping back into the role of lieutenant to help fill the gap left in Company 1. This return shows a strong sense of duty, as a seasoned officer who chooses to serve again despite his age. His behavior on the job is methodical, prudent, and professional, reflecting the experience he gained over years of dealing with dangerous fires and disasters. At the same time, he is known for a steady and reliable personality with a playful side that makes him approachable to those around him.

As a Third Generation pyrokinetic, Onyango can generate and manipulate flames, and he puts this ability to use both in combat and in firefighting operations. Although he plays a supporting role in the larger events of the story, he remains a capable and dependable member of his company, using his fire manipulation to assist in emergencies and to fight when necessary. His development centers on his return to active duty and his continued commitment to his responsibilities as an older officer who refuses to stand aside when his experience is still needed.