彼

Left step radical - the side-form of 行 (walk), picturing a small footstep on the road. The indexing radical, anchors 彼 in the family of motion / path words: 往 go toward, 待 wait, 微 tiny step, 徐 slow. Marks 彼 as relating to direction - pointing to a distant 'that' or 'the other side,' the place you walk toward.

Right 皮 supplies the sound - pí shifting to bǐ with consonant change (b/p alternation is the standard pattern across this phonetic family). Pure phonetic role; the 'skin' meaning contributes nothing semantically. Same phonetic family: 怕 fear, 被 by / quilt, 波 wave, 玻 glass, 破 broken, 疲 tired. 彼此 'each other' is the most common modern compound.