Dual Skill: the theory that an esper can have access to multiple psychic abilities at the same time.
As a theory, there have been no observed cases of such a mutation though many scientists in Academy City pursue the subject with vigor. The recent incident involving Professor Kiyama Harumi has added further enthusiasm to the research. While Kiyama's use of Multi Skill merely "borrowed" abilities from other espers in the Level Upper Network it proved for the first time that the human brain has the capacity to process multiple powers, even those of unrelated types. This eliminated the counterargument proposing that power use is hardwired into the brain- either by genetics or some other, unknown precondition- and is therefore inalterable.