System・Keraunos.
Something that the great achievements of his lifetime and the mystery from a large number of supernatural myths sublimated into.
The ability to manipulate electromagnetism. It possesses such a might, that people are given the impression as if it was the second coming of the Gods of Lightning and Thunder mentioned in a multitude of myths and legends.
Generally, it launches an attack by the means of electromagnetic projection. The existence of this long-distance attack is what qualifies Nikola Tesla, who's originally not a Heroic Spirit that possess a bow or any sort of shooting weapon, as an Archer.