Neku uses psychs, abilities that can be used in battle with pins he equips.

"You were able to use all the pins! You're like some kind of psych genius!" - Shiki

Unlike the other players that he works with, Neku is capable of using a wide range of pins in battle. His ability of easily learning psychs is unknown throughout the story. A safe assumption is that Joshua, being the composer and using Neku for his own personal gain, wanted him to have this skill.

Pins may fall under one of the following categories of psychs:
  Positive: Melee attacks
  Negative: Ranged attacks
  Neutral: Psychokinesis, Pressure Mine, and Irregular Note
  Ability: Fixed effects that do not deal direct damage.

Only a few pins do not conjure abilities or effects that can be used in battle. Neku's psychomancy will prove to be ineffective if pins 246 through 261 are equipped. The respective are specifically for Tin Pin Slammer.