Beast-Class Servant Speculation [GO spoilers]

[Hawkeye]

What beast of regret?

In Chapter 4 of the 7th Singularity, The Old man of the Mountain mentions that, just as Pity (憐憫, Renbin^?) is "one amongst the Evils" (悪の一つ, Aku no Hitotsu^?), so too is Regret (慚愧, Zanki^?, lit. Feelings of Shame / Regret / Repentence). The identity and numerical designation of the Beast that presides over Regret is presently unknown.

I'll admit it's taken from the Wiki, but it was a small enough extract that I figured the odds were good it was accurate.