Hayato Kawajiri

Hayato Kawajiri is a character in Part IV: Diamond is Unbreakable. He is portrayed as an ally to the protagonists and plays a crucial role in the last arc of the story.

Personality
A schoolboy with a knack for science, Hayato tends to spy on his parents with his home-built electronic devices, finding interest in their affairs and conversations.

However, when pressed into a corner, Hayato can prove to be exceptionally brave. Even Josuke has commented on Hayato's bravery when he volunteered to set off Okuyas's explosively-charged body at the risk of death, and expressed surprise that he was a grade school student.

Diamond is Unbreakable
When he spies on his parents with electronic devices on his usual routine, Hayato notices several things highly suspicious about his father Kosaku, who at the time was impersonated by Yoshikage Kira, and almost is killed by Stray Cat in one of his investigations. When he realizes Kira's true identity and becomes cornered by the murderer, he attempts to threaten Kira about having his true identity revealed but is promptly dispatched, hinted at having been killed by Kira, though his death is later rewritten by Kira's time loop.

Hayato then tries seek for help and warn Josuke and his friends of the mass murderer's presence, and first encounters Rohan Kishibe, who is first to fall victim to Killer Queen's Bite the Dust ability. He then wakes up in bed again, having experienced it in a "dream sequence", and realizes that he was trapped in a time loop. He then attempts to avoid Josuke and company, but is accosted by them and tries to hold Bite the Dust off by killing himself with a pencil. However, this reveals Kira's identity as well and Bite the Dust activates, forcing Hayato to realize that he can only rely on himself to unmask Kira. He then exploits the time loop, this time to his advantage, and successfully steals Stray Cat in order to defeat Kira, who finds out Hayato's attempt, cancels his time loop, and gloats in victory. Hayato is, however, saved when his plan to make Josuke Higashikata and Okuyasu Nijimura come earlier work, making both notice Kira gloating and find out his true identity.

During the battle, Hayato plays a major role in assisting Josuke and Okuyasu as a tactician. When Okuyasu is mortally wounded and Josuke conflicted over whether to risk being blown up by using Crazy Diamond's ability to save him, Hayato throws himself at Okuyasu and sets off the bomb. However, this sacrifice does not lead to his death, as Josuke pieces his body back together before he is able to die from being blown apart. When he follows Josuke and they all take shelter in a house, Hayato discovers a photo of Yoshihiro Kira spying on their location in his jacket pocket, enabling Josuke to eliminate Yoshikage's last support. Hayato is among the group of people to witness Yoshikage Kira's death, and is last seen tearfully telling his mom Shinobu Kawajiri he would wait for his father to come home, even though Hayato knows that he is already dead.