After putting up a Bounded Field to clear people out of the forest during the day and retreating back to what he thought was a safe distance, he had made Berserker use her Noble Phantasm.

Its power output was at best C rank, at worst D rank by his estimation. He had used golems he earnestly requested to borrow from Roche as a standard of measurement for its power, but the lightning strikes got weaker the farther they traveled from Berserker, while conversely the golems she hit at point‐blank range had been literally turned into garbage.

Caules estimated that it was powerful enough to kill most Servants if the limiters were released and she fired it from point‐blank range… However, the price for it was too high. There was no proportional gain in killing one enemy Servant at the cost of losing one of their own.

- Vol 2 Chapter 1