Rin Tachibana is a member of the Hachiō Executioner Blade of Yami, the older half brother of Kiyoi Kidou, and the "disciple brother" of Shigure Kōsaka.
Not much in known of Rin's background other than he has a little half-sister named Kiyoi Kidou, who he helps support due to her blindness. At some point, he met a young Shigure when she was playing in the woods and teased her on her skills but praised them for her developed abilities. Once he discovered who her master was, he stated they were now officially disciple siblings and would fight one another when she was strong enough. At some point he joined Yami's weapon's division when he grew up. He was the disciple of Hachirobe Kōsaka.
Rin has long hair in the back and some scruffy bangs in the front. Notably, his face is covered with scars from past battles and wears a large samurai like armor and various weapons.
Rin is a very proud of his skills and is willing to try to get Shigure Kōsaka to join The Hachiō Executioner Blade. Despite not being blood related, Rin has been shown to see Shigure as his fellow disciple and a "disciple sister" of sorts. Because of this, Rin showed a certain amount of care for Shigure, as he was visibly bothered with her interfering in the raid on the government convoys, and even voiced his disapproval of Mihai Ştirbey and other Hachiō members wanting to kill her, saying that she can still be useful to them alive.
Raki Hoshinano, a fellow Hachiō member, even went as far as to question whether or not he was OK with them battling, taking her hostage, and even killing her, knowing the relationship that they have. He even went as far as trying to convince her to join them during her attempt to escape. Despite this relationship however, He is true to his beliefs as a Satsujinken, as he will gladly put his feelings for her aside to achieve his goal and is more than willing to kill her if she continues to get in his way. This was clearly shown as he showed no actual care at all with the treats that were made by Mikumo Kushinada. He stood by her, Isshinsai Ogata, and the rest of the Hachiō Executioner Blade even after the One Shadow Nine Fists members turned on them for their lack of honor and pride. He can also be taunting, as he teased Shigure as a child when they first met about him being able to see up her skirt, which made Shigure embarrassed. He also seems to know Tōchūmaru well enough to immediately recognize him, and to have him locked up alongside Shigure in a box after recapturing her.
While a member of the Hachiō Executioner Blade, Rin has shown to have genuane love towards his younger half sister, Kiyoi Kidou, whom he worries over and helps provide financially for her and wishes for her to be safe by even telling her to leave Japan for her safety. As stated by Kiyou, Rin is a man who will follow his word no matter what.
- Weapons Master: Rin is a master of weapons just like the rest of the Hachiō Executioner Blade. True to his nickname as the "Hundred Martial Arts", not only has he been trained as a samurai, but he has also learned the Kōsaka Style, which is a form of armed ninjutsu that teaches the philosophy and use of all forms of weaponry. This makes Rin not only a master Samurai but a master Ninja as well. As a result, he has mastery over a large amount of weaponry, being able to use this mastery to overwhelm weapon users as skilled as Kagerō Kii and Shigure Kōsaka. Just like his disciple sister Shigure, he is a master practitioner of the Kōsaka Style and is skilled enough to not only go toe-to-toe with Shigure, but to also disarm her, something that no other weapon user has been able to achieve. He is skilled enough to not only perform Shinto Gōrenzan, which is known as the highest level of sword mastery, but is even able to do so using spears as substitutes for actual swords.
- Master Samurai: Despite being a master of the Kōsaka Style, Rin has also been trained in the way of the samurai. As a samurai, he is skilled in the use of swords and other samurai-like weapons as he carries a quiver of swords and spears with him. As a Samurai, Rin has mastered the use of swords and spears, and it has been implied that he has mastered every other form of samurai-themed weaponry as well.
- Immense Strength: Rin has a great amount of strength, as he was able to break the weapon used by Shigure and to smash his way through a wall during his fight with Shigure. He was also shown not to be hindered in battle at all despite wearing heavy samurai armor and carrying a multitude of weapons on his person.
- Immense Speed: Despite wearing a large suit of samurai armor he has enough mobility to match Shigure move-for-move, and is more than fast enough to catch her off guard as well.
He was first seen on the tanker as Shigure fought him all the other members of the Hachiō Executioner Blade members to allow Kenichi and Miu to escape. As Ştirbey prepared to kill her, the Samurai stopped him stating that they needed her alive.
Later, when Shigure attempts to escape, he recognizes Tōchūmaru on her and gives her clothing while she questions how he knows Tōchūmaru. The Hachiō Samurai does not answer, telling her to surrender because it is impossible to escape. Shigure takes a fighting stance with the broken Yami blade she has stolen and the samurai states that he would have to hurt her to subdue her. Shigure charges in towards the samurai and they exchange a flurry of strikes. The samurai compliments Shigure on being able to do so much with only a broken blade, as she is able to jump over him and prepare to escape. They continue to fight as Shigure uses her Kōsaka-Ryū: Tsumujikaze. As the attack is about to hit the samurai, he is able to parry the blow using a technique from the Kōsaka School as well, Kōsaka-Ryū: Yoroigaeshi. The samurai is able to break Shigure's blade but she grabs a weapon from the samurai's quiver, using it to break down a wall.
The samurai is surprised that she was able to steal a weapon from him and Shigure asks the samurai to reveal himself. He says that she has gotten stronger that he had expected and he takes off his helmet. Shigure is surprised as the samurai's face is revealed as Shigure is shocked to see he is her own brother. Rin then takes advantage of Shigure's shock and begins attacking. He reminds Shigure that in the past he had told her if she became extremely skilled with weapons that they one day meet again. They continue to fight till they reach outside where Shigure is shocked to see a large amount of military forces for Yami as Rin explains this is the power Yami has gathered to shack the world and asks Shigure to join them, but she remains unresponsive.
Later, various weapons masters from different countries arrive to help the Hachiō Executioner Blade members and all report to Rin Tachibana who says that the Hachiō Executioner Blade has already partnered with the One Shadow Nine Fists and are fighting all over the world. He proclaims that their time hiding in the shadows is over as the reinforcements raise a battle cry.
He later returns to base and discovers of Shigure's escape. When Raki questions if he's fine with killing her, Rin remains quiet.
Later Rin, along side Mikumo, Sōgetsu, Mildred, Edeltraft, Marmaduke, Ştirbey, Hongō, Agaard, Cyril, Raki, and Ogata all faced off later against the masters and allies of Ryōzanpaku. When the Ryōzanpaku masters attack together against Mildred, it's revealed Kensei only ripped her garmets off below. However, it turns out Kensei injured Rin, Agaard, Ştirbey and destroyed Mildred's bow. When the Ryōzanpaku masters begin to go on the offense, Rin engages battle with them. After Edeltraft splits them all up, Rin was seen fighting Kii to which he questioned why Kii partnered with Ryōzanpaku after his loyalty to Yami. He was surprised that he changed sides due to Shigure having given her the hoe her father made and says he can't let her die and says Rin should die and attempts to attack him.
After Agaard allies himself with Apachai, Rin is attacked by Agaard while Apachai attacks Marmaduke.
After Seitarō uses his Shinto Gōrenzan, Rin and the other weapon users do the same. Rin takes advantage of Sakaki's opening and attacks him from behind but Apachai saves him and incapacitates Rin with a flurry of punches.
Once Yami loses the battle, Rin retreats with everyone else in complete defeat but not before asking Akisame if he can ever meet Shigure again in the future.