Senbonzakura is the manifested spirit of Byakuya Kuchiki's Zanpakuto.

Appearance:
Senbonzakura appears as a masked samurai in full-body armor. He has long, dark brown hair tied with a silver ribbon and wears a golden forehead plate that resembles a half-cherry blossom. From what little is seen from when his mask was broken apart, he appears to resemble Byakuya to some degree.
Personality:
Much like his master, he is portrayed as serious and uninterested in small-talk, as shown when he ignored Ruri'iro Kujaku's attempts at conversation. However, unlike Byakuya, he has occasional emotional outbursts and can be rather impatient. According to Shunsui Kyoraku and Jushiro Ukitake, this is likely a reflection of Byakuya's inner nature from his younger years.  Senbonzakura also cares for Sode no Shirayuki much like Byakuya cares for Rukia. Unlike his partner, Senbonzakura is more cheerful and humble, willing to relax and enjoy partying, even to the point of passing out from too much drinking. He tends to keep his mask on at all times, even while taking a bath, and he also has a spare mask at hand, should his current one break. 

Powers & Abilities:
Master Swordsmanship Specialist: As shown from his short skirmish against Byakuya, one of the most skilled swordsman in the whole of Soul Society, Senbonzakura possesses highly proficient skill.
Enhanced Speed: Senbonzakura has shown tremendous speed. He was able to keep on equal footing with his master, Byakuya, further showing his level of speed.
Immense Spiritual Power: It is stated by Ichigo that Senbonzakura has the same reiatsu as Byakuya, who has immense spiritual pressure.

Zanpakuto:
At anytime, Senbonzakura is able to manifest the sealed sword form of his former self with a square open frame crossguard that resembles a four-pane window.
Shikai: Triggered by the command Scatter (散れ, chire). Shikai Special Ability: In its Shikai, Senbonzakura's blade separates into a thousand slender, tiny blade fragments, which then fly away from the hilt, leaving only the sword's handle in the wielder's hand. Senbonzakura can also transform himself into these many small blades. While the blades are supposedly too small to see normally, they reflect light in such a way as to appear as cherry blossom petals. By swinging the hilt, Senbonzakura can control the blade fragments at will, allowing him to shred opponents at a distance and break through almost any defense.
Bankai: Senbonzakura Kageyoshi (千本桜景厳, Vibrant Display of a Thousand Cherry Blossoms): Senbonzakura drops his sword, then it phases into the ground, as though it were a pool of water. Energy ripples expand outwards, turning the surrounding area dark, and within seconds, two rows of a thousand giant blades rise up from the ground. These thousand swords then scatter into countless flying blades that Senbonzakura can manipulate freely. Bankai Special Ability: Senbonzakura's Bankai has several forms, achieved by arranging the blades in different patterns. Each form presents a different advantage, such as increasing offense at the expense of defense.Senkei (殲景, Massacre Scene; Viz translation: annihilate): This form unites the scattered petals into complete glowing swords, that form four rows.

These rows float just above the other, and circle around Senbonzakura and his opponent in a continuously moving, column-like array. It abandons defense in favor of a concentrated offense. Though visually menacing, this form is not meant for attack from all sides; rather, it is to concentrate his power into fewer blades, thus increasing his attack power. While the swords can be mentally controlled as with his regular blades, he commonly calls them to his hands for actual melee combat. The Senkei also cages himself with his enemy, allowing neither combatant to move very far from each other, though the area is still large enough for maneuverability.Gōkei (吭景, Pivotal Scene): This form organizes the tiny blades into a spherical formation of over 100 million tiny blade fragments, which swirl around the opponent like a cloud. It then flies into them from every possible angle, leaving no blind spots and no possibility to escape.