flutter, flower
茷 centers on the idea of something light and moving: fluttering or waving in the wind, and by extension a flower that sways on its stem.
茷 combines the grass radical 艹 with 伐, which likely contributes a phonetic element. The exact historical development is uncertain, but the combination suggests something plant-like that moves or flutters.
Grass 艹 on top of 伐, which looks like a person with a weapon. Imagine a person cutting grass, and the cut grass flutters away in the wind like flower petals.
For ハイ, picture a flower fluttering high in the sky: high -> ハイ, and the flower waves as it floats upward.