Matahachi Hon'iden (本位田又八) is one of the protagonists and a childhood friend of Musashi.
In Vagabond, Matahachi is portrayed as a cowardly and spineless man. He has a long-held admiration for Musashi from his childhood years, which ultimately builds his growing inferiority complex as an adult. He often tells lies in an effort to better his perpetually dismal situation, which usually leads him to even more trouble. He is also shown to be something of a drunkard and a womanizer, having several sexual partners over the course of the series.
- Osugi Hon'iden: His over protective mother. His mother knew that Matahachi tell lies such as the Sasaki Kojiro name. Before her death, she thought Matahachi can be the kindest person that Musashi or herself can't archieve.
- Miyamoto Musashi: Matahachi considered Musashi to be the closest friend he ever had, but whom he abandoned during a time of crisis. As he grows older, Matahachi constantly thinks of Musashi and develops an inferiority complex as Musashi becomes a famous and skilled swordsman. Matahachi follows Musashi over the course of his journey – a fact which Musashi is unaware of– and often helps Musashi from the shadows when he collapses after a fight or is in danger.
- Otsū: Otsū is Matahachi's ex-fiance and childhood friend, having grown up together with Musashi. However Matahachi was aware that Otsū bonded more with Musashi, and knew that there was a wall between them from the beginning. After he abandons her; the emotional distance between the two increased. After Matahachi saved Musashi, he meets Otsū and proposes to her anew, but Otsū didn't recognise him after their long separation. Matahachi ultimately acknowledges that Otsū loves Musashi and encourages her stay together with Musashi.
- Oko: Matahachi met Oko when he and Musashi set out at the beginning of the manga, and quickly became infatuated with her. The two ultimately eloped, which began Matachi's mother's long search for her son. However, their marriage soured quickly, as Oko grew tired of Matahachi's cowardice. Her job as a prostitute became a source of frustration and jealousy for Matahachi, as she frequently reminded him of his worthlessness compared to her customers. She finally kicks out Matahachi after he accidentaly causes the fire at the Yoshioka school. Though Matahachi later regrets his relationship with Oko, he credits her with teaching him his sexual skills (but also for "spoiling" sex for him, as she was "too good" compared to his later partners).
He was a illegitimate son of a mistress and the previous Hon'iden head, he was born not so long before his father death. The wife of the former head Osugi Hon'iden adopted him as the Hon'iden has no heir.
He later became best friend with Shinmen Takezo, they play together and practiced sword fighting together.
His mother arranged Otsū to become Matahachi's wife.
When Matahachi became 17, he wanted to join the Toyotomi army against the Tokugawa clan at the battle of Sekigahara.
At the beginning of the manga, Matahachi is laying in an abandoned battle field. Along with his long time friend. He had previously left his village of Sakushū with the intention to make a name for himself. He soon discovers that his friend Takezō has also survived that battle, after pretending to be a refugee hunter.
The two proceed to flee the battle field. After walking for quite a while, they stop for a break. They have been walking for three days, and Matahachi expresses his feelings of incompetence. He goes to the bathroom and continues to talk to Takezō. Someone approaches him from behind and puts his sword on his neck. Thinking it to be Takezō pranking him again, he poops on his feet to teach him a lesson. He turns around to see that it is a real refugee hunter, as he cuts Matahachi's arm. Matahachi yells at Takezō to warn him, as Takezō approaches the Refugee hunter. Takezō quickly cuts the man down.
The two evetually shuffle away, Takezō holding him up, as he is hurt. They eventually come to another battle field. A young girl is ringing a small bell. Takezō and Matahachi pass out.
The two wake up the next morning by a small house. Takezō passes out again and awakes inside of it. A japanese women crawls up to Takezo on a wooden floor and asks if he would like a drink. Matahachi tells him to join him also. Takezō, clearly angry, tells him that they're healed and that they're leaving. Matahachi tells him that he must, as they sheltered them for days, even while they were refugees. The women laughs and suggest that the younger girl, who is named Akemi, should choose one of them to marry, so they could both stay there. Akemi doesn't say anything, and Matahachi says that he can't, even though she didn't say anything to him. She leaves and the older women says that she refuses to grow up.
Takezō follows Akemi, leaving Matahachi alone with the other women. They gather mushrooms, but Takezō is less than helpful. Filling his basket unknowingly with poisonous mushrooms. Akemi asks why Takezoō why he doesn't ask her questions. Matahachi has been asking her questions relentlessly, about how they make a living, her age, where her father is, why she is living with her mother alone in the mountains, and why she wears the bells. Takezō asks how old she is, and Akemi tells him that she is fifteen. Suprised, Takezoō admits that that is older then he expected. He tells her that he is seventeen and she reacts the same way, saying that she thought he was around thirty. Akemi asks Takezoō if he has anymore questions, and he asks her what she was doing when she found them in the field.
Back at the house, Matahachi is apperently looking through their house. he finds a large amount of swords stshed away. The woman walks in as he is looking through them. Meanwhile, Akemi admits that they're thieves. Akemi's mother tells Matahachi that they go to every battle field, after the fighting is over, and collect swords, armour and anything they can sell for money. They strip them of of the corpses, and that's how they make money.
A man approaches Akemi and Takezō. She throws rocks at him and he addresses her by name.
It was revealed through Oko that after they abandon Musashi, Matahachi married Oko and worked at a castle construction site carrying stones. Oko forced Matahachi to send a letter to Otsu ending his relationship with Otsu. According to Oko, she was fed up with Matahachi's low income so she opened a whore house working as a prostitute. Matahachi ended up as a pitiful alcoholic with Oko bringing in most of the money for the couple.
As Matahachi returns back to the whore house, he revealed to Oko and Akemi that Musashi was still alive and he challenge the Yoshioka School. Oko kicks Matahachi out and told him to never come back as she wants to break all ties with an arsonist.
Matahachi left Kyoto and ended up working as carrying stones for castle construction. While he was resting on a break, he encountered Tenki who saw Matahachi's pale face and gave him medicine. In return, he asked Matahachi to look out for government soldiers if they're coming. Some soldier found out that he was drawing a map and they thought Tenki was a spy. Tenki ended up half dead as he took down 5 soldiers, Matahachi was ordered to watch over him until the soldier returns. Dying, Tenki with his last breath begged Matahachi to deliver something.
Matahachi checks Tenki belonging and found some money and a swordsmanship certificate for Sasaki Kojiro who mastered the Chujo Style. He assumes that Tenki is Kojiro and decides to go on a journey to deliver his belonging to his parents. As he journeys, instead for looking for Kanemaki Jisai; he decides to look for Toda Seigan in Osaka but it turned out fruitless. He was told that it was better looking for Ito Ittosai, Matahachi gave up as Ittosai hasn't been seen for some time. Matahachi stayed in Osaka with the intention to be hired by the government, while drinking he attracted a ronin called Akakabe Yasoma. Matahachi accidently named himself as Kojiro, Akakabe took advantage of Matahachi and cheated his money. After realizing he was fooled, he went after Akakabe and killed him, he assumes Sasaki Kojiro's identity.
Later, after coming into contact with the genuine Kojiro, begins to identify himself as Sasaki Koujiro, an interpreter for Kojiro, as the real Kojiro was deaf and had difficulty communicating with others.
Matahachi later becomes estranged from Musashi after a tense reunion, displaying an intense jealousy towards his former friend.
After his mother's death, Matahachi decides to follow his original journey to hand over the certificate to Kojiro. Unexpectedly Matachi found out that Kojiro has become very popular and a swordsmanship instructor.
The story is set in the future showing him to be at a older age. He became a storyteller telling stories about Musashi and Kojiro. Although he only knows mostly Kojiros story but he can easily guess what Musashi has been doing over the years. He hesitated on telling the infamous duel between Musashi and Kojiro.
- Matahachi's character is based on one of the same name in Eiji Yoshikawa's novel, on which Vagabond is based. Matahachi plays largely the same role and has many of the same problems, but there are significant differences. In the novel, he doesn't interfere in Musashi's fights nor did the two of them get into a fight. In fact, the two remains good friends in the novel and encourages each other. At one point, they even travel together a second time following a Buddhist priest. Eventually, Matachi requests that Musashi marries Otsu and, later, he goes to Kokura with his wife and child in order to pray for Musashi's victory over Kojiro.
- In the novel, Matahachi eventually repents for his ways and starts a family. Surprisingly, his wife is not Oko, but her daughter, Akemi. The two gets into and out of relationships several times, but their relationship seem to solidfy when Matahachi encounters Akemi after his repentence and finds her taking care of a child he believe is his.