He is brave, fearless and somewhat reckless, which was shown when he attacks a Four Horsemen of John while ignoring orders. It is noted not to be the first time. Yu is often called an idiot by those who know him. He is a very narrow-minded person, whose goal is to annihilate all of the vampires because of what they did to his "family," and he will overcome any type of challenge in order to accomplish it. He swore to kill all vampires because they killed Mika.

   Despite this, he has a soft spot and worries about his friends first and his goals second. Ferid Bathory considers this attitude to be "cute". Because of this, he empathizes with others who put their family first, as seen when a civilian girl gave his squad false information because vampires are holding her family hostage. After learning why she deceived them, he tells the girl that she did the right thing to save her family. He feels guilty for abandoning Mika and has nightmares about Mika's death for four years until he makes friends with Shinoa and Yoichi. After learning Mika is alive, Yuichiro's personality changes in response and he grows more mature, as noted by Shinoa. He puts more effort into being patient and calm and making friends, and immediately amends his worldview to include Mika even though he is a vampire. His dream of wiping out vampires takes second place to reclaiming Mika. Regardless, even though his best friend is now a vampire, Yū still slaughters them without mercy or hesitation. After Shinjuku, he becomes closer to his squad members and makes Guren promise to help him take Mika back under the promise that Mika will be useful to him, as he comes from the same orphanage as Yu. Additionally, friendship and bonds become more important to him, as shown in a mental battle against Asuramaru, to gain more power or else lose his body, he calls Asuramaru his friend and convinces Asuramaru to yield to him.

    Rather than revenge, his primary goal changes to protecting his new "family," in order to avoid a repeat of past events. In Nagoya, he surprises Narumi's squad by memorizing all of their names and promising to protect them.

    Similarly to how vampires do not bother to remember human faces and only think of them as "humans" or "livestock," Yu only sees vampires as "vampires" or "bloodsuckers" without bothering to remember their names or faces. He does not even recall the name of his vampire target in Nagoya. The only exception to this rule is Mikaela Hyakuya, and seems to recognize Ferid Bathory.

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