- Japanese Voice Actor: Kengo Kawanishi
- English Voice Actor: Griffin Burns
- Age: 14
- Manga Debut: Chapter 44
- Anime Debut: Episode 21
- Race: Human
- Gender: Female
- Status: Deceased
Muichiro and his twin brother, Yuichiro, have a woodcutter father and a mother who is a housewife. Their mother caught a cold that developed into bronchitis when they were 10. Their father went to look for medicinal herbs and was caught in the storm and died.
Soon after, the twins became orphans. Muichiro started looking after the two of them. The spring after they became orphans, they were visited by Amane Ubuyashiki and were invited to join the Corps.
Muichiro was excited to join the Corps, but his brother opposed this. Yuichiro would even chase Amane away, hoping she would stop inviting them to join the Corps. Yuichiro even blamed their parents for their deaths.
He said that they died because of their selfless nature, and they should not be like that. Then, one night, they were attacked by demons. Yuichiro lost his left arm while protecting his brother. Muichiro used all the tools he could find to fight the demon.
When the sun rises, the demon turns to ash. When Muichiro returns to their house, his brother is almost dead. Yuichiro was praying that his brother would survive. Muichiro then lay beside his brother until he died. When Amane and his daughters arrive later, they nurse the wounds of Muichiro.
He then loses his memories of the past. He joined the Demon Slayer Corps and became a Hashira in only two months. Despite not having memories of his past, he has deep anger toward demons which has been his driving force while in the Corps.
Muichiro started having the cold personality of his brother when he was in the Corps. He is dreamy and just cannot be bothered. As Tengen would recall, his extraordinary skills are arguably one of the best in the Demon Slayer Corps. In the Swordsmith Village, Muichiro would be seen arguing with Kotetsu.
When he was not given the key to Yoriichi Type Zero, he slapped Kotetsu. Tanjiro intervened and was surprised when Muichiro, with a petite frame and thin arms, would not even budge.
Muichiro would constantly quarrel with Tanjiro while staying in the Swordsmith Village. If he were not in dispute with him, he would be using the mechanical doll, Yoriichi Type Zero, to practice. After staying for a week in the village, they would face two upper-rank demons.
While he battles Hantengu and Gyokko, he has a flash of memories. While in the middle of the fight, Muichiro’s blade broke. His new swordsmith, Kozo Kanamori, then handed him a new blade.
During his battle with Upper Moon 4 and Upper Moon 5, Muichiro was able to awaken his Demon Slayer Mark. Muichiro, along with Tanjiro and Mitsuri, defeated the upper-rank demons. Muichiro was poisoned, but he checked on Kotetsu first before collapsing.
Tanjiro and Muichiro later thanked each other for what they did for each other during the battle. Muichiro also regains his lost memories. Mitsuri then pulls them together for a group hug. The next time they will meet will be during the Hashira training.
Before the training started, Muichiro was interviewed regarding what happened in the village. He was asked about the Upper Ranks and how he was doing. He later explained about the poison he got from Gyokko, how it rendered him immobile, and he used breaths to slow down the effect.
He also explained how he got his mark and thought his body was 39 degrees Celsius when he got the spot. Later, Muichiro was given the task of training the other members of the Corps with their movement.
He will be training them with coordination techniques. When Tanjiro arrived on his training grounds, Muichiro became friendly and complimented him. This is not something he had done with anybody. He calls the other members of the Corps useless and incapable.
The Hashira training was proven effective when Demon Slayer Corps fought against Muzan and his minions. Muichiro was killed in a battle against Kukoshibo.
The long straight hair that reaches to his waist compliments Muichiro’s pale complexion. He has a short stature, and his hair is loose in two clumps. These clumps would protrude slightly on both sides of his head. His mint-green eyes are large and empty looking.
Muichiro looks the same as his twin brother Yuichiro. His Demon Slayer uniform is longer and has looser sleeves. The uniform is dark and slightly turquoise-tinted. His pants do not have bands around the calves. He wears dark blue tabi socks and a pair of white zori with white blue socks.
Muichiro is an airhead, impassive and selfish individual. Before his memory loss, he used to be warm and happy, but he got his brother’s personality after losing his memory. He is one of the most devoted members of the Corps. However, he does not care about people around him and dislikes talking or mingling with them.
He cares for the Oyakata and even flicks Tanjiro’s forehead to talk back to Kagaya. However, he has a violent side that he would gladly show to humans and demons alike. He looks down on people who do not have the same skill set as him.
Being able to rise to the rank of a Hashira for only two months after joining the Corps. He even easily overpowers the demon slayers who are older than him. His reflexes, speed, and endurance are some of the best in the Corps.
To be able to fight two upper ranks and hold them back at the same time only shows his skill set. When he was fighting Kukoshibo, he was praised by him for his swordsmanship and fighting ability.
Muichiro was one of the first few to awaken his Demon Slayer Mark. When he battled with Kukoshibo, he dyed his Nichirin Sword bright red, and he was able to use a transparent world. His endurance is extraordinary, and this was shown when half of his body was already cut, and he was still able to turn his bright sword red.
His willpower is one of the main reasons for his extraordinary strength. Losing his twin brother to the demon when they could barely fight back contributes to his rage.