Little is known of Hayao's Zanpakutō. Due to his extensive training sessions, he has mastered hand-to-hand combat, so he needs to rarely use his Zanpakutō. What is known is that it would appear that he is one of very few Shinigami to own two Zanpakutō. Further information will be added when it is made available.
Hayao has been brought to 4th Division’s quarters to be healed on numerous occasions throughout his lifetime. Most of these visits do stent from his training growing up (rumor has it that he has trained under a total of three different Captains or former Captains). On one of the incidents in which Hayao was brought it was from his childhood. It is said that he sustained a fall, landing hard on the floor below. Although he was cleared without issues, his attitude seemed to change after the fall.
Timeline as a Shinigami:
He was trained under former 2nd Division Captain Yoruichi Shihōin, becoming one of her best pupils and youngest to master the “Flash Cry” technique. Age 5-8
He trained under former 12th Division Captain Kisuke Urahara, he learned to not only summon his Zanpakutō spirit, but achieved Bankai level in less time than his father. Age 8-10
He trained under 5th Division Captain Shinji Hirako in order to learn how to master the powers of his “Hollowification”. Age 10-11
He trained under 5th Division Lieutenant Momo Hinamori in the use of kidō. Age 11-12
He trained under 4th Division Captain Retsu Unohana in the different uses of medical kidō. Age 12-13
??? Age 13-16 (Between this time period, Hayao’s location was not known, but he was not within the Soul Society)
He graduated within a year after entering the Shinigami Academy. Age 16
He is the youngest Shinigami to be accepted into The Secret Remote Squad. Age 17
Despite his young age, Hayao has proven himself to be a perfect addition to the 2nd Court Guard Squad. His speed is rumored to even surpass that of Yoruichi Shihōin, one of his former teachers. It would appear that the two have a very close relationship, despite her not being an officer within any of the 13 Court Guard Squads. He has been known to help out with paperwork passed down from the higher ranks (mainly that of Captain Soi Fon). He wears a coat that resembles that in which the Captains would wear. It is unknown where he received this coat, but it appears that even Genryūsai Shigekuni Yamamoto (Captain of the 1st Court Guard Squad and leader of the Gotei 13) allows him to wear it. He has a close relationship with his twin sister (Hoku Kurosaki), the two often competing back and forth with one another. Hayao has been known to wear weights while training to continue to increase his speed (it is currently unknown at what weight he is currently carrying). Hayao’s hand-to-hand skills are among the best within the Soul Society, having been trained by who most consider to be the best hand-to-hand fighter (Yoruichi Shihōin).