Nagumo Yoichi is Guest's younger brother. A precious family bond shared since childhood. Probably precious. Actually, they've bickered quite a lot since they were young. Given they come from a family of spies, one might expect a quiet upbringing, but as killers, they grew up hitting and beating each other (though Guest won every time) and hurling insults. But the older he gets, the more creepy this Nagumo Yoichi becomes. He grew up too much... He was cute when he was little.