Hm.

[quote=F/CMIV Profile]Misty Night Murderer - Rank A:
As a murderer rather than an assassin, she can strike before her victim. However, she can only unconditionally take the first strike at night. During the day, a luck roll is required. Jack the Ripper's victims are believed to have all been attacked while off-guard.[/quote]
If it's just "strike before the victim", I think you could make a case for the Master's Servant being able to react to it if they're close enough to their Master (the victim) since the Servant isn't the target? 

But then again there's this bit too:

[quote=Same as the First]
Presence Concealment - Rank A+:
A skill that suppresses presence as a Servant, suitable for covert action. If presence were fully suppressed, she would be nearly impossible to detect. However, when prepared to attack, Presence Concealment's rank falls substantially. [b]This weakness is compensated for with "Misty Night Murderer", allowing for a perfect surprise attack.[/b]
[/quote]

Though tbh if we just ignore the highlighted bit, it wouldn't be that broke.