KanjiJLPT N3
Reformation

reformation, change, modify, mend, renew, examine, inspect, search

Mnemonic

A snake had been poisoning the village wells for years. A ninja captured it and, rather than slaying the beast, retrained it to guard the water supply. The villagers called this miraculous change the great reformation — a deadly serpent turned protector by the ninja's discipline.
Additional thoughts
Picture the snake coiled protectively around the village well, its fangs now bared only at intruders. The ninja stands behind it, arms folded — reform through patience, not destruction. Left side of the kanji is the snake; right side is the ninja's striking hand enacting change.
Quick recall
A snake is retrained by a ninja into a village guardian — a true reformation.

Details

The keyword for 改 is reformation. This kanji conveys the idea of changing something for the better, correcting, or renewing. It encompasses the act of revising, amending, or overhauling systems, behaviors, or conditions in order to improve them. The character is broadly used in contexts involving reform, revision, and renewal, carrying a sense of deliberate transformation toward a more desirable state.
On'yomi
かい
Kun'yomi
あらた.める、あらた.まる