Kei (also known as Braslota III) was the uninhabited third planet in the Braslota system. This system, which was in the Oneamisu sector, was selected by Starfleet Command in 2365 as the location for the battle simulation Operation Lovely Angel.
In the simulation, the starships USS Hathaway and USS Enterprise-D had simulated objectives that either ship had to complete before progressing to the next objective. In the first objective, either ship would attempt a successful capture of control of near-planetary space in the region of Yuri, while, at the same time, maintaining a defensive posture from a simulated threat from Kei.
Kei was labeled on a diagram of the Braslota system. In this diagram, the planet's position and orbital path were depicted. This diagram was on display in the observation lounge of the USS Enterprise-D. (TNG: "Peak Performance", okudagram)