Jūgo's Clan's Kekkei Genkai

Members of Jūgo's clan have unique bodies, which allows them to passively absorb natural energy. This allows them to transform parts of their bodies for several purposes. However, due to the constant absorption, they sporadically feel sudden, uncontrollable urges to kill, causing them to go on a rage. While varied in purpose and function, the body transformations occasioned by this ability are similar looking in that a pattern covers the affected area as the transformation occurs, the skin on the affected area turns brown, and if the transformation occurs in the eyes, their sclerae turns dark as well.

Unlike most others who train in senjutsu, the members of this clan are not required to stay still in order to absorb the natural energy around them. They are also not vulnerable to petrification, despite the constant influx of natural energy.

Background
After Jūgo massacred an entire village during one of his rages, he secluded himself, living in caves, until he was approached by Kimimaro, who told him Orochimaru could help him with his urges. Jūgo went to Orochimaru voluntarily, and allowed him to research his transformations. More interested in the source of the transformation than in curbing the killing urges, Orochimaru experimented with Jūgo's body fluids, developing an enzyme that can trigger similar changes in other, suitable hosts, through cursed seals, which Orochimaru determined to be 10% of the population, all others dying after having the cursed seal applied. However, their transformations are limited to fixed forms, able only to transform into a specific form back and forth. His investigations on the source of their power also lead him to the discovery of Ryūchi Cave.

After Sasuke absorbed Orochimaru, Kabuto Yakushi found himself without purpose, and following Orochimaru's belief of adding to himself to find his true self, injected himself with the biological material of the subjects of many of Orochimaru's experiments, including Jūgo. Doing his all to emulate his master, Kabuto went to the Ryūchi Cave, and the ability to absorb natural energy passively aided him in training senjutsu under the White Snake Sage.