Yu Yu Hakusho's power system is Spirit Energy (Reikin). Both humans and demons can cultivate spirit energy into devastating attacks. The tier system goes from F-Class through S-Class demons.

Demon Power Classes

ClassDescription
D-ClassWeakest demons — easily handled by Spirit Detectives
C-ClassMid-tier. Most named antagonists in early arcs
B-ClassPowerful. Dark Tournament competitors
A-ClassElite. S-Class boundary approaches here
S-ClassThe absolute ceiling — existence threatens both realms

Spirit Gun

Yusuke's signature technique — concentrated spirit energy fired from his index finger. Ranges from a small blast to a city-destroying beam depending on his power level and emotional state.

Demon Heritage

Later revelations show Yusuke has demon ancestry. His awakened demon form unlocks power beyond S-Class measurement.