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