|Sergio "Hellgate" Cocteau|
|Melee Weapon||Murasame Mk 9|
|Ranged Weapon||EZ Nashorn III|
|Accessory Weapon||Unknown Handgun A|
Sergio "Hellgate" Cocteau is a shield class Sinner, and one of the protagonist's companions.
Sergio is a veteran Sinner with realistic, if not brutal, expectations and views of the world. He mentors other Sinners, always telling them to watch their backs on the battlefield and giving constant warnings to the Protagonist about not letting their progress get to their head, which can sound rather pessimistic. He seems to be friends with Uwe, as well as Nina and Kai, who both speak fondly of him.
The Protagonist meets Sergio during the party hosted by Nina and Uwe after the protagonist and Mattias survive their first operation against other sinners. Like Uwe, he is a veteran sinner who mentors other less-experienced sinners.
He doesn't have a role in the story outside of giving hints and opinions to the protagonist in the Fueling Station and help them out on missions as a companion.
- He, alongside Nina, Marie, Shizuka, Kai and Billy have no role in the story outside of being companions.
- Sergio is voiced by Hiroki Goto