改悪
かいあく · kaiaku · JLPT N1 · noun
changing for the worse
改 = change + 悪 = bad: a change that makes things worse
改 (kai) means change or reform, as in 改革 (kaikaku, reform). Adding 悪 (aku, bad or evil) flips the meaning to change for the worse.
改 — 己 (self) + 攴/攵 (action/strike)
改 is a compound of 己 'self' and 攵 (the action radical, originally a hand holding a stick). The image is of striking or applying force to oneself or one's situation, suggesting reform or correction. From this came the modern meaning 'to change, alter, correct'.