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|“||As shinobi, we must always put our lives on the line in battle. If you're going to seek mercy from your enemy, you have no business in Nabari.||„|
|~ Kouichi Aizawa|
Kouichi Aizawa is one of the main protagonists of the manga/anime series Nabari no Ou. He is a student and classmate of Miharu Rokujo who studies ninja techniques under Tobari Durandal Kumohira. It is later revealed that he is actually an immortal owl in human form. His immortality is attributed to the holder of the Shinra Banshou during the Edo Period, who was a medical practitioner that experimented with animals, placing the wisdom of the Shinra Banshou in them.
Kouichi is quite a tall young man with a lean muscled build from his training as a shinobi. He has white messy hair that matches the feathers in his animal form, and wine-red eyes on which he has a pair of oval-shaped glasses.
|“||It's said life is powerful because there's death in everything. As humans, we long for death. I don't want to just sit here as my parents, Miharu, you Raimei and you Sensei grow old and die. I couldn't handle it. All I want is to be freed from this curse. I'm terribly afraid of being alone.||„|
|~ Kouichi's opinion of his immortality|
However, Kouichi also has a dark side; during confrontations with other shinobi, he is highly pragmatic and merciless, never hesitating to kill and even stating that in Nabari, it's kill or be killed. This side of him is noted by Raimei, who never guessed that such a nice person could be so ruthless. When fighting, he maintains an eerily calm demeanour, and often smiles after killing someone. A notable example of this is when he shoots Mr. Frosty dead with a gun and then smiles like nothing happened, an action that shocks even the apathetic Miharu. Because of this ruthless nature, Kouichi is usually the one to call out Tobari for his inability to take a life, especially since it makes his mission of protecting Miharu difficult. As far as Kouichi is concerned, a person who can't protect the people close to them is no different from a murderer.
Having been around since the Edo period, Kouichi is highly intelligent, displaying extensive knowledge of various ninjitsu techniques as well as the world of Nabari. He has a slightly morbid fascination with death, due to the fact that he couldn't die even if he wanted to. Having lived for centuries, Kouichi has grown to view his immortality as a curse and wishes to be free from it, saying that he's tired of everyone he knows and loves dying around him while he lives on, since he hates being alone, showing that he truly cherishes his friends in spite of his ruthless nature.
In addition to his morbid fascination with death, Kouichi also has a rather dark sense of humour, one example of this being when he willingly falls over the side of the cliff. When Raimei and Tobari grab him out of shock, Kouichi laughs at both of them, saying that he wasn't in any danger since there's no way the fall could have killed him. In general, Kouichi tends to react to any horrifying situation very calmly, likely because he's seen it all due to being alive for so long.
In contrast to Tobari, who is determined to keep Miharu from ever using the Shinra Banshou, Kouichi is rather conflicted about whether or not he wants Miharu to use it; on one hand, he wants to be mortal again, and sees the Shinra Banshou as the perfect way to become such. However, the Shinra Banshou is also the reason he became immortal in the first place, so he can also sympathise with Tobari's desire to have it sealed away forever, so it'll never bother anyone again. Overtime in the manga, however, he decides to help Miharu become strong enough to use the Shinra Banshou, having decided that there's no other way for him to lose his immortality. In the anime, however, this doesn't happen and he is content with living out his life as "Kouichi Aizawa".