Hirofumi Yoshida/History

International Assassins arc
Upon finding out that Denji's existence has been revealed through the media, Makima orders her subordinates to get several Public Safety Devil Hunters and hires Yoshida to protect Denji from the onslaught of assassins targeting him from all over the world for one month. Makima later introduces Yoshida, Kusakabe, and Tamaoki to Denji as part of his personal security. In the present, Yoshida and the other Devil Hunters meet up with Denji and Power at a park, ready to head towards the site where the assassins are located.

At a burger restaurant, the group waits for Denji and Power to finish eating before heading out. They soon meet up with Kobeni, Galgali, and "Kurose", who is actually the eldest brother of the American Thugs disguised as him. He attempts to deceive the group, only for Power to accidentally kill him by ramming Kobeni's car into him and Denji.

Seeing that the eldest brother's disguise has deactivated, Yoshida deduces that the three brothers have a contract with the Skin Devil, and notes that there are only two brothers left. Shortly afterwards, Yoshida tracks down and swiftly executes Joey in an alleyway before rejoining his group.

The next day, the group find themselves targeted by various assassins sent to obtain Denji's heart. Inside an empty mall, the Public Safety Hunters fend off Santa Claus's doll army as they ascend the building. However, Quanxi ambushes the group, swiftly taking them down one by one.

Yoshida fights Quanxi with the help of the Octopus Devil but ends up getting knocked unconscious. Before Quanxi can kill Yoshida, Kishibe arrives with two of Quanxi's Fiends restrained. This causes Quanxi to stop her assault, and Kishibe attempts to convince the former to join his secret plan to kill Makima.

She denies this offer, and the conflict resumes as Aldo, the youngest of the American Thugs, attempts to shoot down the group. As the situation becomes more chaotic, Yoshida recovers and decides to have a rematch with Quanxi, holding her off while Beam takes Denji to safety.

They exchange blows, with Quanxi initially having the upper hand, but Yoshida is able to land a powerful kick on her face, damaging her. After some more fighting, Quanxi defeats Yoshida and throws him out of the building. As he falls, Yoshida manages to catch himself with the Octopus Devil. Upon regrouping with Kishibe, Yoshida reacts with horror upon seeing the descending colossal hand of the Hell Devil snatching everyone inside the mall away to Hell at Santa Claus's request.

Yoshida and Kishibe later finish off the remaining Dolls while discussing about Makima and her ulterior motives for her actions. Kishibe then asks whether she can hear them, to which Yoshida reveals that Makima can only borrow hearing from lower forms of life. The veteran Devil Hunter warns Yoshida to not involve himself with things he shouldn't be concerned with.

Once Santa Claus is defeated, Yoshida and Kishibe approach Quanxi, who has decapitated Denji from behind. The two men put on blindfolds, concealing their view as Makima kills Quanxi and her remaining two Fiends. Taking off his blindfold, Yoshida asks Kishibe if he is going to take it off, to which the latter solemnly replies that he doesn't want to see a thing. Afterwards, Yoshida returns to his high school to finish his finals.

Justice Devil arc
As Asa Mitaka attends Fourth East High School under the order of the War Devil, she meets Yoshida, who asks if she needs to go to the nurse's office. Yoru possesses her and asks Yoshida for information regarding Chainsaw Man's whereabouts at the school.

Yoshida tells Yoru that since he recently transferred to the school, he has no idea. Yoru also asks Yoshida to be her boyfriend, to which the latter rejects her in response. After Asa joins the Devil Hunter Club, he becomes one of the members of her group.

Yoshida later finds Denji watching a news reporter and attempts to convince him not to publicly reveal his identity as Chainsaw Man, saying that he is following Denji on a mission from his organization.

At school, Yoshida finds students paying Denji to sit on him and returns Denji's student ID card to him after Denji purposefully left it at the scene of his fight with the Cockroach Devil. To appease Denji's wish for a girlfriend, Yoshida introduces him to Asa, which fails miserably.

Later, Yoshida recovers Denji with the Octopus Devil after he defeats Yuko to stop him from revealing his identity. Upon retrieving Denji, Yoshida warns him that he made it clear he will use force if necessary.

Dating Denji arc
Yoshida appears at the aquarium where Denji and Asa were having their date alongside the Devil Hunter Club. Upon being noticed by Denji, he claims that he also happened to be there at the same time as them when they were trapped by the reincarnated Eternity Devil.

Led by Haruka Iseumi, the group then attempts to find a way to escape the endless aquarium, but they cannot find anything useful, unfortunately. Yoshida also witnesses Asa's failed attempt to prove herself useful to the Devil Hunter Club after the latter briefly argues with Denji.

Three days later, Yoshida tells Denji that, due to everyone inside the aquarium slowly losing their minds, this should be his cue to do something to fix their current situation. Denji tells Yoshida that the only reason he was able to kill the Eternity Devil in his first fight with it was that it revealed itself to him, but since the devil is nowhere to be found, he is unable to do anything. Denji then asks Yoshida if he is able to do something, to which Yoshida pulls out a cell phone.

However, Yoshida tells him that getting just one signal is not enough to get a call for help and theorizes that due to the power of the Eternity Devil, time has effectively stopped in the outside world, making any effort to call useless. Noting that Seigi and the other Devil Hunter Club member have both snapped in their own way, he also tells Denji that he is okay with dying before asking him if Chainsaw Man would be able to eat the Death Devil for the good of the people, which makes Denji think that he has also lost his mind.

After Asa breaks them out of the endless aquarium, Yoshida mockingly remarks that the Eternity Devil has helped him appreciate life more as he helps Asa kill it. As Fami remarks how her plan to help Asa turn Denji into a weapon with the Eternity Devil has failed, Yoshida notices and locks eyes with her, engaging in a staredown with an unknown outcome.

Falling Devil arc
After Asa appears to have been stood up by Denji at school, Yoshida approaches her once again and asks her to accompany him for a bit, taking her to the Devil Hunter Clubroom. Having heard Asa's ramblings, Yoshida agrees with her notion that life is easier alone. He then tells her to stay away from Denji and leaves without an explanation.

Yoshida then approaches Fami, aware of her identity as the Famine Devil. He tells her about an urban legend concerning a prophecy of Nostradamus predicting the end of humanity in July 1999, and Public Safety believes that whatever Fami is planning is connected. Yoshida threatens Fami to talk, and she tells him about the recent appearance of a Primal Devil.

Current arc
After the battle of Denji and Asa Mitaka against the Falling Devil, Yoshida sends a squad to put Nayuta in custody and kidnaps Denji taking him to a secret location. He tells him that Asa is in the hospital alongside other civilians and Nayuta and her dogs were taken into custody. Yoshida says that he doesn't have to worry about them, as long as he behaves and does exactly what he tells him to do. He then takes Denji to the location of a violent protest in his name and gives him a final warning making him decide to never transform as Chainsaw Man again or else Nayuta will be murdered by Public Safety.

Some time later, at school, Yoshida finds out Denji has been blamed for a fight between two students. He says that he doesn't know the exact details and is not interested in knowing them. He then invites Denji to skip classes and go to watch a movie to cheer him up.

Yoshida eventually comes to fight against Asa and Yoru and manages to cut their arm off. After Yoru becomes stronger by the recent increase of fear to War, Yoshida fails at cutting off Asa's other arm, she stands up and turns back to Yoru, she fails the attack and Yoshida takes this opportunity to retreat.