User blog comment:Xilinoc/Ch. 543 - Letters/@comment-5809522-20130628065502

On the subject of the Stern Ritter's letters, I have my own educated guesses on what some of them are; I think Mask's letter stands for 'The Strength' (since he mainly used brute strength the whole time), the other masked guy, BG9, I think his letter may stand for 'The Kill' (kinda random, but since he fought Sui-Feng, it's the best guess I can come up with). As for Yhwach's letter, I have a good feeling it might be something along the lines of 'The Absolute', but I guess we'll learn soon enough...