Koroshiya 1

In Shinjuku Kabuki-Cho, the biggest sin town in Japan, there are two crazy guys. Ichi is a coward and a wimp, but once he breaks into tears, he turns into a human weapon. With great martial arts skill and a blade hidden in his boots, he butchers a bunch of enemies into mincemeat in the blink of an eye. His arch enemy is Kakihara, a yakuza boss who's tired of everything, including himself. Only when he pierces, cuts, and burns his own and other people's bodies does he feel that he is alive.

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Prequel: Ichi
http://www.mangago.me/read-manga/ichi-yamamoto-hideo/
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