User blog comment:Xilinoc/Ch. 599 - Too Early To Win, Too Late To Know/@comment-493809-20141002132603

I doubt the special letters will be used, partially because I don't think they exist in Romaji or English. Maybe there'll be an extra four Stern Lectors show up later and teach Ichigo a cruel lesson.

If not, I'm going with most people and guessing Shaz is under the hood. After all, when's the last time Ichigo deliberately killed someone with a name? Hint: it's a guy who was confirmed to still be alive (sorta).

I still have that theory of Yhwach = Starrk, which also puts the mental image in my head of all the Sternritter finally being killed, Yhwach confronting the Soul King, and saying "I am not alone" while going Captain Quincy Planet.