I see it like this. You are Xion. The human monk. Through ritual and devotion to your art, at the conclusion of sad ritual, yu let forth a BLOODY ROAR !!! And your flesh changes for the first time. Your bones grow and your flesh is ripped from your skin by the expanding bone. Your brain is all that is left in your metalic boned body. You are now Xion the wereundead!
There is only a hybrid form, no "full undead" and in this form you gain benifits of undead and some str and dex increases or sumtin like that. but you transorm back to a living human when done. in human forn, cure heals. in Xion form inflict heals. so on and so forth . . .