Vrex

Vrex is a planet located in the same star system as its neighbor Stai, in the the galaxy's Alpha or Beta Quadrant.

History and specifics
Vrex is a Galactic Union planet used for indoctrination and training. Its main facility imbued children from member planets with the philosophies, loyalties, and skill sets desired by the Union. In the 23rd century, that included how to wage war. Equipment included a brainwashing device.

In 2266, the USS Enterprise (NCC-1701) arrived in orbit of Vrex. Captain James T. Kirk sent a landing party down to the surface in four space bugs to recover Staian children kept there to enforce Stai's membership in the Union. When his personnel were imprisoned, Kirk beamed down with reinforcements. However, they were also captured, and Union patrolman Ruf brainwashed Kirk. A rescue party led by Spock was able to reverse the effects on Kirk and the children, then destroy the device. The Staian children were returned to Stai. 

Points of interest

 * Indoctrination facility
 * Brainwashing machine