Decim is the bartender of Quindecim and an acting arbiter for the dead. He always puts up a serious face and is very cool and professional. His hobby is putting dummies together and dressing them up. He has a lot of respect for people who lived fulfilled lives.
In the latter episodes, it is revealed that he is Nona's test subject. Although he is an arbiter and therefore a dummy, she gave him human emotions, and she is testing and watching him. These emotions are interfering with his judgement and his profession as an arbiter, making him question the system of judgement.
Anime boys come in all sorts of different hair colors; each one with their own charm and set of cliches/tropes. This time, let's focus our attention on white haired anime boys who tend to be a little bishi-er than most.