Shikotsumyaku

is the Kekkei Genkai of the extinct Kaguya clan, which gave them the ability to manipulate their own skeletal structure. By infusing their calcium with chakra, they can manipulate the growth and properties of their bones to their likings. Users of this ability could protrude their bones out through their skin with any injuries that would be received during this process healing instantly, change their bone density, and could even completely regenerate a lost bone. The ability seems to be rare amongst the clan members, as Kimimaro was the only one to exhibit it out of his entire clan.

Apparently, this ability gives the user a unique body, as when Kimimaro was fatally ill, Kabuto Yakushi claimed there had been too little information on his body to give any medical treatment.

Abilities
The main capabilities of the Shikotsumyaku is allowing the users to manipulate their bones' growth. This allows them to create weapons of bones that can be either protrude from any part of the body, or pulled out and used like hand held weapons. They can even fire pieces of their bones as long-ranged projectiles.

Also, the users can intensify the density of the created bones, making them stronger than steel. This not only makes the created weapons very powerful, but also makes their bodies virtually indestructible, as any point of contact on the body could become as sharp as a spear tip, giving them a nearly perfect defense, as well as having an intensely hard armor.

From what the only known user of this ability, Kimimaro, has shown, most of the techniques are named after flowers. Most of them are also taijutsu-based sword dances, which are used for close combat and defenses. However, as Kimimaro demonstrated, the bones can also be forced to grow from the ground, as a form of a ninjutsu, and that he can emerge from any of these bones.