Buchse was a sharpshooter for the Belfar Agency, working under Geschutz. Although their priority mission was to reclaim the Chronicle of Fierce Regalia, Geschutz would eventually decide to prioritize fighting the threat of the Order, by collaborating with the Company.
Buchse was an extremely quite person who rarely spoke or expressed any emotion. However, during his time with the Company, he was tickled by Tsaubern and giggled. He was so humiliated by this, he fired his gun at the next person who entered his room, almost hitting the hero, who he mistook for Tsaubern.
It could be unconnected to that incident, but after the war, Buchse was withdrawn from the Belfar Agency and assigned to Ritterschild's noble Halnish family as their new captain of the guard. Apparently, the head of the Halnish family had somehow taken a shine to him.