KanjiJLPT N1
Enlighten

disclose, open, say

Mnemonic

Behind a door, a ninja kneels in shadow. He opens his mouth and whispers ancient secrets meant to enlighten you — suddenly the darkness lifts and understanding floods in like sunlight through the opened door. The ninja vanishes, but his words still echo from your mouth, enlightening all who listen.
Additional thoughts
Picture a sliding door cracking open, revealing a crouching ninja whose glowing mouth emits beams of wisdom. Door = barrier to knowledge, ninja = hidden master, mouth = spoken teaching that breaks through ignorance.
Quick recall
A ninja behind a door opens his mouth to enlighten you with whispered wisdom.

Details

The keyword for 啓 is enlighten. This kanji conveys the idea of opening up someone's mind, guiding them toward understanding, or revealing knowledge that was previously hidden. It carries a sense of instruction, education, and intellectual awakening. It is often associated with the act of teaching or imparting wisdom to dispel ignorance.
On'yomi
けい
Kun'yomi
ひら.く、さと.す

Used in vocab