Fennel works as an armor repair technician for the Kaburagi Group, serving as a senior colleague to Natsume. He possesses short green hair and yellow eyes, typically attired in a white shirt and gray pants while on duty. His personality is flippant and flirtatious, marked by womanizing tendencies. He frequently pressures Natsume into social outings like dinner invitations, framed as welcome parties, which she consistently rejects. His unsolicited physical contact, such as massages, causes her visible discomfort, heightened by Natsume's status as a teenager.

Fennel exhibits cowardice under pressure, panicking during critical moments like a Gadoll attack when his gear malfunctioned. In his panic, he attempted to climb onto a coworker's seat, resulting in both falling from Deca-Dence's exterior and inadvertently causing Kaburagi and Natsume to fall with them. This incident led to the death of his coworker; Fennel fainted and was rescued by Kaburagi.

Traumatized by this event, Fennel abandoned exterior repair work entirely, restricting himself solely to indoor maintenance duties due to his fear of combat situations. His skill set is limited; he possesses no combat abilities, and his aptitude for armor repair remains subpar despite four years of experience. Much of his previous work involved menial tasks like clearing Gadoll meat residue from the fortress walls.

Fennel harbors an unreciprocated romantic interest in Natsume, persistently inviting her to dinner and offering unwelcome physical contact. Natsume actively avoids his overtures and shows no indication of returning his feelings. He occasionally offers supportive gestures, like encouraging her to ask Kaburagi for a welcome party, though these align with his attempts to ingratiate himself. His role remains secondary, primarily illustrating the daily lives and social dynamics within the maintenance crew, with no significant character development or narrative evolution beyond his retreat to indoor work documented across official media.