raincoat
襏 centers on a protective garment worn against rain: a raincoat.
襏 combines the clothing radical 衤 with 發, which likely contributes the sound. The character is specifically associated with a raincoat.
The left side 衤 is clothing, and the right side 發 looks like a complex covering. Picture a heavy raincoat made of many layers that you put on when the rain starts.
For ハツ, imagine putting on a raincoat and hearing the rain go 'hats, hats' against the fabric: hats -> ハツ.