aggressiveness; combativeness; fighting spirit
Describes a strong, often defiant or competitive, forward-facing attitude. Common in phrases like 向こう意気が強い.
He has a strong fighting spirit and will take on any opponent.
Sometimes aggressiveness alone isn't enough to win.
負けん気 is a strong dislike of losing, often stubbornness, whereas 向こう意気 is broader aggressiveness or combativeness.
Compound of 向こう (mukō, 'opposite side, facing') and 意気 (iki, 'spirit, heart'). The exact historical derivation is uncertain, but it conveys a spirit that faces or confronts the other side.