Kosaku Kawajiri (川尻 浩作 Kawajiri Kōsaku) is a minor character featured in Diamond Is Unbreakable.
He is murdered by Yoshikage Kira to preserve his "quiet lifestyle" and escape justice. After his death, Kira masqueraded as Kosaku and integrated himself into Kosaku's family and life.
Kosaku apparently has an identical body structure and size to Yoshikage Kira but has slightly bigger feet. Upon introduction, his facial features and a patch of his hair were removed by Cinderella.
Based on Yoshikage Kira's appearance after stealing his appearance, he had spiky black hair, thin, dark eyes, and higher cheekbones than Kira.
Kosaku is never seen alive, but, according to his wife, he was a cowardly man who was never prepared to pay the rent on his house and got bossed around at work even though he worked every day. Kosaku did not get along with his son very well. He also hated his wife's food. Described as someone who would not talk if angry, he would never ask for forgiveness and hated Shinobu's cat, locking him outside of their house so he would not enter at night.
Kosaku had no unhealthy habits such as smoking nor drinking. According to his wife and son, he was "boring" and disliked mushrooms.
He was introduced to Shinobu by her friends in middle school, and she dated him because it made her feel superior to them. At some point she became pregnant, obligating them to get married.
Diamond Is Unbreakable
Kosaku was on his way home from work at the same time Yoshikage Kira was fleeing Josuke and his friends. Picking Kosaku out of the crowd because of their similar build, he dragged him into Aya Tsuji's salon and killed him. He then forced Aya to switch his and Kosaku's face and fingerprints. His body is then completely disposed of. After evading his pursuers, Kira assumed Kosaku's identity and started living with his family.
When Kira dies, he does so under his original identity, meaning that the death of Kosaku is not public knowledge.