Originally a foot stepping out from a baseline — meaning 'to go to.' The walking-foot picture was later borrowed for the homophonous grammatical particle (possessive 'of' and object pronoun), now its dominant use. The 3-stroke modern shape is the brushed silhouette of that single moving foot, filed under Kangxi #4 丿 (piě) by stroke pattern.
Filed under radical 丿 (piě, #4) by convention. 丿 is not a separate component in 之, so no strokes are highlighted.
