reins, saddle cover
鞁 centers on horse tack made of leather: specifically reins and a saddle cover, both items that control or protect the horse.
鞁 combines 革 (leather) with 皮 (skin/hide), both related to animal skin, to express leather horse tack such as reins and saddle covers.
Leather 革 and hide 皮 together make the leather gear used to control a horse: reins and a saddle cover.
For ヒ, imagine a horse hee-hawing as you pull the leather reins: hee -> ヒ, and the sound reminds you of the horse tack.