TSO is said to have performed experiments on Sentrakh in an attempt to make the DHs more loyal, but in the process his state of being was changed so that he inhabits a "shadow state" between life and death. Also, in the Dark Hunter book, TSO says that "[p]erhaps someday, if I am feeling charitable, I will free him from his current empty existence . . . and repay his gift of life with my gift of death," which seems to mean TSO could remove Sentrakh from his shadow state and kill him whenever he wanted. How do you think this was achieved?
One idea that's sort of out there is that TSO assigned Sentrakh to protect him (to make that his final goal in life), then made Sentrakh don a Mask of Undeath before somehow siphoning all of his life force into it, killing him. Then, when Sentrakh came back, he would have all the life force he did while living, but would be wholly dedicated to TSO. This would also explain how TSO could release Sentrakh from his shadow state and kill him: by simply removing his Kanohi. Of course, there is one large problem with this theory: Sentrakh doesn't wear a Kanohi... perhaps it is fused to his head?
Edited by Infrared, Jan 19 2014 - 02:19 PM.