Justin's personality can be described as polite and zealous. He is seen smiling numerous times in the series and addresses his peers and enemies with suffixes. He does not openly look down on anyone, nor chastises them, yet is prepared to kill should he be given the orders by Shinigami.
One of Justin's most notable characteristics is his devout faith in Shinigami to whom prays and give thanks for everything. His faith affects the clothes he wears and how he typically speaks, using chiefly religious terms even within his normal sentences.
Another characteristic is his earphones, which he is never seen without and has the volume of the music turned up rather high. The volume is so high, it prevents him from hearing when people speak to him. Because of this, or out of necessity, Justin has the ability to read lips, but due to his constant usage of earphones and Shinigami wearing a mask, he cannot understand Shinigami. This also applies to Tezca Tlipoca, who spoke to Justin on several occasions in the past but never realized that Justin could not actually hear him. Another drawback is that he tends to speak loudly due to his constant use of headphones. This also annoys other people who are not aware that he is capable of reading lips, leading them to think that he is ignoring them.