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As a child, Hiro had a bad relationship with his father, who would punish him for misbehaving, while never punishing his two daughters. Hiro grew to hate his father and tried as hard as he could to ruin his life, by causing trouble in school, skipping classes, continually getting bad grades and getting into fights outside of schol hours. At the time, Hiro didn't seem to notice that his behaviour was also hurting his mother, who he loved. When Hiro was fifteen years old, his father was killed in a train crash. After this, Hiro realised the pain he had always caused his family, and began to regret his actions. He wishes he had more happy memories of his father, instead of only bad ones, and blames himself for his mother's unstable mental health.

Hiro takes out his anger at himself by drinking a lot and picking up older women for sex (once he becomes more well-known as a member of VivieNne, he tends to pick up fangirls instead). This behaviour doesn't help the atmosphere at home between him and his mother and sisters.

He often puts on a front and doesn't let his friends know how he really feels, although he occasionally opens up to Yuki, after a few drinks, and spends hours crying about everything he regrets. He spends more time as Yuki's apartment than he does at home.

He joined VivieNne after being recommended by Yuki, who remembered him as a good guitarist on the occasions he turned up to his music lessons in school. Akemi feels that Hiro's behaviour is often extreme, but isn't one to judge and doesn't let it create a problem between them.

Hiro has his first "girlfriend" (despite having slept with numerous women beforehand) in Yoshi, who practically forces herself on him, insisting she is his number one fan. He likes her enthusiasm for him and decides to keep her around for a while. He isn't serious about her and is mostly using her for sex, but she is very serious about him and insists she won't let him 'escape' if he tries to dump her.

Hiro later makes a good friend in Soshi (read: Hiro later becomes a terrible influence on Soshi) and drags him into his unhealthy lifestyle.