Kei's an android... I can't really say too much about his past without spoiling it for the Tsuki readers, but he ended up fighting and losing to Goten in one of my fanfics, so Trunks decided to reprogram him. If you want to know more about Kei's past, then I suggest you just read through Tsuki.

Personality wise, Kei's usually cold and silent. He's very intelligent, and tires quickly of LTAG and Risa's antics. He doesn't appear much around the site, as he'd probably just stand in the corner and say nothing.