Sensei

Sensei is a Japanese word which means "Someone's elder" and is often used as an honorific for teachers.

In the Warhammer 40,000 universe, the Sensei are supposedly the immortal offspring of the God-Emperor of Mankind, left over from the time when he was walking around and living as a man. In the good ole' days of the fluff, their end goal was to achieve apotheosis and merge their souls with the fragment of the Emperor floating around in the warp - the Star Child. They were also all blanks.

The Black Library writers got sick of them. To that end, they were later revealed to be unwitting dupes of Tzeentch and were unceremoniously purged by the Inquisition.