dense
丯 centers on the idea of dense, tangled, or disordered growth, like thick vegetation or a chaotic mess. The single given meaning 'dense' captures this sense of tightly packed confusion.
The exact historical development of 丯 is uncertain. It may be a pictograph of tangled vegetation or a simplified representation of dense, chaotic growth.
The vertical line ｜ is overgrown with slanted strokes 彡 on the right, like a plant stem choked by dense, tangled leaves.
For カイ, imagine a dense, chaotic tangle of vines that you need to cut through with a sharp 'kai' sound: kai -> カイ, as you hack through the dense growth.