Baishin is a middle aged, grey-haired man with a beard and blades growing out of his shoulders. He has two red marks on his forehead. He wears a samurai-like armor over his Shinigami hakama. 
Baishin appears to be a violent man who would kill anyone around him in an uncontrollable rampage. This is actually due to him fusing with his own Zanpakutō in an attempt to further his swordsmanship, which he could not reverse the effects of. Wanting to separate with his blade at any cost, Baishin sought powerful individuals in order to absorb their Reiryoku in order to trigger an explosion strong enough to achieve his goal, even if it meant his own death. Because of this, when Ichigo slashed him in half and killed him, Baishin died happily as it split him and his Zanpakutō apart.
400 years prior to Ichigo gaining Rukia's power, Baishin found a way to merge with his Zanpakutō, in his attempt to further his swordsmanship. However, he could not return to his normal form, and as a result he went on a rampage. He became responsible for the death of 63 seated officers, some of which were lieutenants, and proceeded to escape to the Human World. A total of six captains were sent to capture him, two of which lost their lives while the remainder were able to imprison him in a statue.
The Sealed Sword Frenzy
Baishin eventually breaks free from the statue where he was sealed, killing everyone in the area while doing so. He proceeds to hunt down those with powerful Reiatsu. He confronts Renji Abarai and Ichigo Kurosaki. Renji shoots him, but it has no effect and he gets stabbed with a blade. Ichigo, transforming into a Shinigami, begins to fight Baishin. As Ichigo attacks, Baishin grabs him and takes some of Ichigo's Reiatsu. Renji and Rukia Kuchiki attack, but they are too weak to hurt him. Just at that moment, Tōshirō Hitsugaya shows up and scares away Baishin. Before Baishin leaves, he unleashes a bunch of Hollows.
Traced to the site where he was once sealed, Ichigo releases his Reiatsu to track down Baishin. Baishin once again fights Ichigo, this time with Rukia and Renji at Ichigo's side. However, by sucking out Ichigo's Reiatsu, Baishin is able to perform his final release. Baishin summons his Bankai, which transforms his skin into metal, becoming a living being of swords. He is eventually killed by Ichigo using his own Bankai. After Baishin dies, Ichigo reveals that Baishin had merged with his Zanpakutō. Yoruichi thinks that Baishin tried to use Ichigo's Reiatsu to return himself back to normal, separating his body and his Zanpakutō, even if he perished. The only thing left of Baishin is the Zanpakutō he once merged with.
Powers and Abilities
Master Swordsman: Baishin technically is a sword. Before he permanently fused with his Zanpakutō, Baishin was a highly skilled Shinigami. Desiring to become more powerful, he fused with his Zanpakutō as it was seemingly the only way to gain more power. He cut down lieutenants and any seated officer that got in his way, killing a total of 63 Shinigami. After escaping to the Human World, he managed to kill two captains before he was sealed.
Immense Spiritual Power: Baishin has an immense amount of spiritual energy. After he absorbed some of Ichigo's vast spiritual energy, his spiritual power became even stronger than before. His Reiatsu is red.
Enhanced Durability: Baishin was unfazed by a level 31 Destruction Spell, unscathed by Zabimaru's Higa Zekkō, and was even able to deflect Hitsugaya's Hyōrinmaru with little to no effort. He also blocked Zangetsu with his hand without effort or injury. This durability increased on a scale of 5-10 folds after his Bankai was released.
Having merged with his Zanpakutō, Baishin is capable of transforming his arms into blades. He can then fire them at his opponents, allowing him to fight both at close combat and at a distance. Baishin seems to have the ability to call upon Hollows, but it may just be that they are attracted to him because of his spiritual energy. Upon his death, the Zanpakutō that he merged with was the only thing that remained; it is an ordinary katana with a rectangular guard, and a serrated edge of rectangular blades.
- Shikai: The name and release command of his Zanpakutō are unknown due to him having merged with his Zanpakutō.
- Bankai: During the battle with Ichigo, after absorbing a large amount of the former's energy, he is able to release his Bankai. In his Bankai form, Baishin's body becomes covered with hundreds of blades that act as both a weapon and armor. The golden rings appear ranging from his right shoulder to his right upper arm, and seemingly a small wing composed of entirely blades is also present on the left side of his body. He has the ability to shoot these blades to great effect. 
- "I am a Blade."
- Bleach OVA; Sealed Sword Frenzy