Hyorinmaru is the manifested spirit of Toshiro Hitsugaya's Zanpakuto.

Appearance:
Hyorinmaru in Dragon Form.The spirit of Hyorinmaru is that of a gigantic, ice blue, serpentine ice dragon with large wings and an echoing voice. Hitsugaya has had a close connection to his blade since first awakening his Shinigami powers. Before Tōshirō began training to control his Shinigami powers and leaking reiatsu, Hyōrinmaru would constantly appear in his dreams in an icy landscape (most likely Toshiro's inner world) and call out to him, although Tōshirō was still not able to hear him. Hitsugaya's inner world is seen as an icy landscape easily accessible to him as he enters into a meditative state.Hyōrinmaru' true form appears as a tall, young man with long, wild, teal green hair, an icy blue X across the center of his face, and gray eyes. In his human form, Hyōrinmaru appears as a stoic and silent man dressed in loose samurai-like garments, a chain around his waist (similar to his Zanpakutō form) and a dull gold adornment on his chest (similar to the design on Hitsugaya's sash). His arms and legs are covered in ice, similar to Tōshirō when using Bankai, and he has a prehensile tail with an icy tip. At any time, Hyōrinmaru can take the form of a gigantic, icy blue, serpentine dragon with large wings and an echoing voice.

Personality:
He is portrayed as calm and silent, only speaking when it is something of importance, as shown when talking to Ichigo. His composure is great enough to even put up with the juvenile antics of his fellow Zanpakuto spirits, even when he is caught in the middle of it. Unlike the other manifested Zanpakuto spirits, Hyōrinmaru does not remember his name or his master. His reason for rebelling against the Shinigami is to find the place where he and his power can be understood. He seems to have a slightly humorous side to him as well. During one of the anime omakes, Isane Kotetsu steps in to check up on Toshiro while he was still recovering from his battle only to find the flowers, the basket of fruit, the curtains, and his blanket frozen. Also, there were two statues of Tōshirō and Hyōrinmaru bowing down to him, while he asks Isane casually if something was the matter. After being scolded by her, and having all of the ice removed, Hyōrinmaru simply says his release command and freezes the room again, this time completely, shocking Isane.

Powers and Abilities:
Master Swordsmanship Specialist: While only seen for a few seconds, Hyorinmaru demonstrated impressive skill from effortlessly being able to block Ikkaku Madarame's attempted attack on Muramasa, as well as being capable of easily countering the attacks from Hitsugaya, a captain level Shinigami.
Immense Spiritual Power: Hyōrinmaru stated that his power is so vast only a truly powerful Shinigami could wield him thus saying he has enormous spiritual power. This is also proven as he was able to easily break through Hitsugaya's Kidō spell.
Enhanced Speed: Hyōrinmaru has shown to move at tremendous speeds. He is able to surprise Hitsugaya with his speed, thus showing the level of his speed.
Ice Manipulation: Hyōrinmaru is the strongest of all ice-element Zanpakutō in Soul Society. He has the power to control any/all ice and water. The power it expels is so overwhelming that in Soul Society, its mere release affects the weather within the immediate vicinity, creating a thunderstorm or a blizzard. His control is so great, Hyōrinmaru is able to freeze anything he comes in contact with and can instantly perform any of his ice techniques. 

Zanpakuto:
At any time, Hyōrinmaru can manifest the Shikai form of his form self. It is a sword with a long blade, star-shaped tsuba, and a crescent-shaped blade attached to its hilt by a long metal chain, which can extend greatly if necessary by force of will. The chain itself can be used as an attack or to entangle a target.

Shikai Special Ability: His slashes can create an immense amount of spiritual power which overflows from the tip of the blade, creating a flow of ice shaped like a Chinese dragon. The dragon flies towards opponents and instantly freezes anything it touches. Hyorinmaru can create multiple ice dragons to attack an opponent from various angles. He can also further manipulate these dragons to surround a target.  Hyorinmaru can also direct his slashes towards the ground and form a wave of ice which rushes over his opponents, overwhelming and freezing them. The chain-blade also freezes anything Hyōrinmaru traps with it. The power it expels is so overwhelming that in Soul Society, its mere release affects the weather within the immediate vicinity, creating a thunderstorm or a blizzard.

Sennen Hyoro (千年氷牢, Thousand Years' Ice Prison): Hyōrinmaru creates many ice pillars which encircle him or and his enemy. At his command (when he turns his sword 90 degrees counter-clockwise), these pillars then move towards the enemy, enveloping and crushing it.Bankai: Daiguren Hyōrinmaru (大紅蓮 氷輪丸, Great Crimson Lotus Ice Ring): Hyorinmaru can transform into a gigantic, icy blue, serpentine dragon with large wings. It is capable of firing a beam of ice from its mouth, which is powerful enough to temporarily freeze Ryūjin Jakka's flames.