Ring of Four

The Ring of Four (四の輪, Yon no Wa) is one of the Royal Ring of Five Guards in the Royal Special Task Force (aka, the Royal Guard). The Ring of Four are unique to the in that they share some of the responsibilities of the Ring of Three and the Ring of Five. Like the other Royal Ring of Five Guards, the Ring of Four are powerful, but less experienced or inadequate to higher position due to personal flaws, such as brashness or impulsiveness. Like the Ring of Three, the members of the Ring of Four are not authorized to enter the royal palace, to see the royal family, or to see the Spirit King.

Special Duties
The duties of the Ring of Four haven't been explicitly stated, however, one of their jobs is to patrol Seireitei to keep an eye on the Shinigami.

Headquarters
The Ring of Four's HQ is a large building complex located just outside the King's Palace. It is essentially a small town that possess everything the Ring of Four needs to operate.

Recruitment
Traditionally, all members of the Royal Special Task Force were former captains of the Gotei 13. Kirio Hikifune, who was a former Captain of the Twelfth Division, and Takashi Ishigawa, who was a former Captain of the Tenth Division,were two such members. However, exceptions were known to have been made, such as the case of Kazuki Ashira, better known as Ashira the Deserter, and Naoki Kawaguchi, a medicinal prodigy. Kazuki's appointment was outside of the traditional cycle of only captains being recruited into the Royal Guard.