Gilbert, before coming to FRIAR, was stationed at the Glasgow Branch with his superior, Kate, and Haruomi, his close friend. On a certain mission, they encountered a Rufus Caligula which damaged Kate's God Arc armlet and escaped after she pierced it with her broken God Arc. In order to stop herself from mutating, Kate asked Gilbert to kill her which he did and had to devour her with his God Arc. This incident created rumors of Gilbert as a superior killer, "Fragging Gil". A few years later, Gilbert is recruited into Blood and becomes Romeo's foil in behavior often at ends against each other. After the Friar arrives at Anagura, Gilbert reunites with Haruomi who had been transferred to the Far East Branch as 4th Unit's new captain. Soon after the reunion, Rufus Caligula appears again so Gilbert, the Protagonist, and Haruomi hunt it down once and for all which then awakens Gilbert's Blood Power and Blood Art potential. Later on, Gilbert confronts Romeo's decreased morale by telling him to quit fighting if he can't keep up.