Kazuhiro Ishii is the oldest child and only son of Takumi Ishii and his wife.

Shin Gaiden Benizakura Hen

Kazuhiro lives with his parents in Sannohe. He goes to inform his parents when Chako's puppies are born. He wishes Chako's puppies could become fighting dogs but his father says they're too small.

Because the biggest puppy is greedy and doesn't let his siblings to suckle milk, Kazuhiro puts the puppy inside a box every day so that the other puppies have time to suckle. He isn't at all unhappy when the puppy is taken away by his uncle.

As months pass, Kazuhiro keeps walking the other puppies named Benizakura and Jirokichi. One day, Aoshima attacks Jirokichi but Benizakura saves his brother. Kazuhiro goes to apologize mister Aoshima along with his father but Aoshima tells there is no reason to apologize and that Benizakura could become a fighting dog.

Aoshima starts to train Benizakura with Kazuhiro. It seems like Aoshima eventually became the full owner and trainer of Benizakura and Kazuhiro didn't move with them anymore.