foe, enemy, revenge, grudge, feud
冦 centers on hostile opposition: a foe or enemy, and the lasting negative feelings that come with it—revenge, grudges, and feuds.
冦 is a variant form of 寇, which combines 宀 (roof) with 元 (head) and 攵 (hand holding a stick), suggesting a person striking another under a roof—an invader or enemy. The modern form 冦 replaces 宀 with 冖 and simplifies the lower part.
Under a cover 冖, a head 元 is struck by a hand holding a stick (the lower right part resembles 又, a hand). This is an enemy attack, leading to revenge and grudges.
For コウ, imagine a foe holding a grudge and shouting 'KOU!' as they strike: the sharp sound 'KOU' cues コウ, and the attack fits the kanji's meaning.