反～
はん～ · han～ · JLPT N2 · noun
anti
🧲 反 = turn back, so 反対 = turned back, opposite; anti- and counter- follow
Like a magnet's reversed poles, 反 flips a word's sense. 反応 is a turned-back reply (reaction), and 反論 is an argument turned back (rebuttal).
反 — hand 又 under cliff 厂
Originally a pictograph of a hand (又) turning something over against a cliff or slope (厂), depicting the action of flipping or reversing. From this came the core meaning 'to turn over,' which extended to 'opposite,' 'contrary,' and 'rebel against.' The character is purely semantic, with no phonetic component.