|This article is about a/an transformation device in Kamen Rider Black and Kamen Rider Black RX.|
There are two King Stones, one for each Century King. When Kotaro and Nobuhiko were both kidnapped, they were each infused with one of the King Stones. However, Kotaro escapes becoming a Century King thanks to the intervention of his stepfather, Soichiro, and takes up the identity of Kamen Rider BLACK. Nobuhiko is not so lucky, however, and becomes the perfect Century King; Shadow Moon.
In order to transform into Black, Kotaro crouches down, cracking his knuckles. He then crosses his arms individually into the air, before circling them into a pose. He then shouts "Henshin!" causing the belt to materialize itself in several red & white flashes. His Rider form then materializes in a shade of green, and the BLACK logo etches itself into his armor to complete the transformation and refine the armor's features. The King Stone is also the energy source for BLACK's finishing moves, the Rider Punch, Rider Kick, and his unique King Stone Flash technique.
In Kamen Rider Black RX, Kotaro's King Stone responded to Kohtaro's crisis and by absorbing sunlight, became the Sunriser (サンライザー Sanraisā). The Sunriser is BLACK RX's transformation belt. In response to BLACK's evolution, Sunriser enables Kotaro to communicate telepathically and use sunlight to power RX up. That factor places RX at a disadvantage while in an area devoid of sunlight. The Sunriser also allows for Form Change, changing its design to suit the form, as well as providing RX with versatility.
- The King Stone had gained the ability to talk to Kotaro after he evolved into RX, but only used this ability twice. &