Apart from his obsession for Sonia. Kazuichi has a very interesting and back story where we learn that he was once bullied and even betrayed by his friends which led him to change his appearance as he is now. Upon their first meeting, Kazuichi was very hesitant to consider Hajime a friend. Cautious about the "friends" he had beforehand, he didn't want to be betrayed again. It did take some time, and quite a bit of Kazu giving Hajime the silent treatment, thinking he's the traitor, for Kazuichi to finally open up to Hajime. For Kazu, Hajime is pretty much a blessing. Hajime seemed to be the first person to put up with his crazy antics, and accept him. Better yet, not betray him.