ka（カッ）
ka describes a sudden, sharp widening of the eyes, used to mark an instantaneous shift in emotion or focus.
kusu-kusu（クスクス）
kusu-kusu describes a soft, restrained form of laughter, typically a quiet chuckle or giggle made under one’s breath.
koro-koro（コロコロ）
1. Rolling lightly
kira（キラ）
1. A brief flash or sparkle of light
kiraan（キラーン）
1. A sharp, sparkling flash of light
kira-kira（キラキラ）
kira-kira is a Japanese mimetic word that describes a sparkling or glittering visual quality.