I believe I've read the entire manga up to somewhere in the Fullbring arc, but I'll happily accept any reminders or pointers.
Also, here's hoping this is all acceptable. I don't particularly know now Japanese adjectives work, nor do I have a big vocabulary for them, so I didn't really know how to say '[Fractured/Split] Dragon'.
Name: ISHIMATSU noburo (石松翔)
Appearance: Ishimatsu's mask is a humanoid draconic face, one side white, the other black, the visible fangs, eyes, and horns of which are shades of grey opposite one another. He typically wears his Jacks robes open over an otherwise bare torso, over which his mask hangs by a light chain when he's not wearing it. His lower half is adorned with the loose-fitting garb of the Gotei 13, a minor difference being the lack of troublesome footwear.
Noburo's face is a rough thing, with broad features and a distinctly claw-made scar on the left side. His hair is grey, with no particular hue to it, and he keeps it just short enough to stay out of his eyes, which are themselves heterochromatic; dark and light. He's of roughly average height, and an athletic build, with obvious physical discipline.
Personality: Ishimatsu Noburo is someone who learns best from experience, and loves competition, seeing it as the natural extension of that learning style. He is somewhat self-centered, but also has a deep respect for fairness and honesty. Between the two, he resents secrecy, particularly that of the Jakakumei. Noburo also has difficulty caring about anything that he can't translate into a game, or anything that bores him. He's a bit mouthy, as well, eager to start an argument or a duel with anyone if it seems like it'll prove entertaining, and happy to test antagonizing an opponent as a strategy.
History: Rather than one of the original members of Nobunaga's squad, Noburo is the son of Ishimatsu Kanna, one of the founders of Jakakumei. The identity of his father, in contrast, is not known, his mother's reasoning being that as long as the man was a smart, powerful warrior -- which, who the fuck was this bastard whose ass she'd just whipped to questioned her? -- then her kid would turn out okay.
As it happened, Noburo turned out just as loud-mouthed and confrontational as his mother, but also just as clever, and just as good with a sword. He spent his childhood mostly around fighters, and the original Jacks in particular, and as a result, decided that more adult activities like fighting and strategy were what he should be playing. His repeatedly challenging the high-ranking Jacks at the tender age of 50 had varying results, but over all, the boy caught an instinct for dueling in its many forms.
As he passed neared adulthood though, Noburo realized that his views and those of the Jakakumei didn't entirely match. He cared less and less about avenging the revered Nobunaga, and more about improving his skill in combat. Eventually, he left his family, the Jacks, and went out into Soul Society to train himself, rather than aid what he felt a lost cause. In this time he entered the Shinigami Academy, learning the techniques taught by the supposed enemies of the Jakakumei. His distinctive childhood left Noburo far more talented with swordsmanship than the rest of his age group -- though he had virtually no talent for Kido -- and he graduated the Academy early, entering Zaraki Kenpachi's 11th Division due to his disposition and skillset.
During this time, Ishimatsu also made contact with his Zanpakuto for the first time, and unlocked the Shikai form. He routinely went on missions to slay hollows in the human realm, and rose through the ranks of 11, until he was among the top 20. Slaying hollows, however, grew to bore the shinigami. The near-mindless beasts were not real opponents, after all; they had no strategy, no skill. Finally, Nobura realized that killing hollows would never give him the challenge he so craved.
During this stage of his life, Nobura grew progressively more lax in his duties, being more obsessed with dueling his peers. He was finally posted in the human world, where he wouldn't have the opportunity to challenge his fellows. The Meiji revolution proved an entertaining enough distraction for a time, but Nobura was jealous of their fights. Finally, he had a chance encounter with someone in a blue robe, which he immediately recognized. On conversing with the Jack, Noburo learned that his mother had died some decades previously. Considering his options, the shinigami elected to retire from the Gotei 13, and head back to his family. The transition was awkward, but Noburo was at least accepted as an ally.
Zanpakuto: Fractured Dragon - When sealed, a longsword with a painfully bright and reflective blade, guard, hilt, and pommel. The scabbard is a dark, unreflective metal, the same weight as the sword. The Zanpakuto's spirit is split into two dragons whose personalities match and contrast each other. If Ichimatsu enters the sword's domain, he generally encounters the two engaged in competition, whether it be physical combat or games of strategy.
Shikai: 'Balance, Fractured Dragon' - Noburo draws the sealed sword from its sheath, and the two parts transform into matching longswords, one white, the blade of which gives off faint light, the other black, which is unreflective and very slightly transparent. The white sword can burst explosive force or steadily stream outward pressure, and the black sword does the opposite. In addition, the stronger the use of their force, the more light the white sword gives off, and the more translucent the black sword becomes. The only things not effected by the force of the blades are Noburo and the swords themselves.
Bankai: Not yet revealed to others.
Other Skills: While often lazy, Ishimatsu is a keen strategist when he puts his mind to it, and works to understand an opponent fully while 'playing' against them. When he's idle, Noburo's mind tends to gravitate to either mental reviews of previous challenges, or philosophical musings on the nature of competition. As a hobby, he reads arguments between philosophers, whether they be from the spirit or human world, and as such is quite familiar with the various arguments between such people, despite his otherwise brutish affectations.