Right-side
艮 supplies the sound — gěn shifting to hěn in
狠 (g/h alternation in this phonetic series).
艮 carries a faint semantic flavor of 'stubborn, immovable' which suits the unyielding cruelty of
狠. Phonetic family:
很 (very),
恨 (hate),
痕 (scar),
跟 (heel/with),
根 (root).