The Shugoryuu (守護竜 lit. Guardian Dragon) are a group of Shinigami and Vizard who have gained the ability to morph into dragons.
Becoming a Shugoryuu
Shugoryuu are rare beings because of how they are created. To become one a person must ingest an Iwa no Ryuu (岩竜 lit. Rock of the Dragons), a rare rock found only in Riku no Hatsu. Once ingested, at 8 AM, the time period other Shugoryuu call Tatsunokoku (辰の刻 lit. Hour of the Dragon), the ingestor passes out. During this time their body slowly turns for the first time into a dragon.
Once they awaken they are trapped in dragon form for at least an hour after regaining consciousness. During this time period, they can at times lose their sentience and will; normally rampage out of control. After this, they must learn to dominate their new powers or else be consumed by it forever.
Zanpakuto: When transformed, a Shugoryuu's blade is found grafted to their tail when sealed in blade form. When they release their blade, it can be found in their hands, grafted to their wing talons, or still be found on their tails. Zanpakuto abilities are not hindered, but enhanced by a Shugoryuu's dragon form.
Inshikokyuu: (因子呼吸 lit. Elemental Breath) Shugoryuu naturally have the ability to breath an element; usually the element corresponding to their zanpakuto. Though they can learn to breath other elements, they will not be as strong as their natural one.
Hollow Masks: If a vizard becomes a Shugoryuu, they can still call upon their hollow masks while in dragon form. The mask will have the same design, but will be shaped to accomodate a dragon's head.
Osame (納め lit. The Closing): This technique isn't related to a Shugoryuu's dragon form. It is normally discovered after many years as a Shugoryuu, and is either useful on or off the battlefield. Each Osame is different, and once unlocked it can be freely used without a word. Osame usually gives a Shugoryuu a new technique, or a new trait (i.e. wings while in human form).
The Shugoryuu have some weaknesses in dragon form. Those with scales are not armored on their stomachs. Some naturally don't have scales, which is useful for stealth, but not head on fighting. Also, though they can morph between dragon and human form at will, it takes great concentration, which can cause some Shugoryuu to be trapped in either form when they are unable to concentrate.