KanjiJLPT N1
Endure

endure, bear, put up with, conceal, secrete, spy, sneak

Mnemonic

A blade presses directly against your heart. The pain is unbearable, yet you must endure. Imagine a ninja initiation: a razor-sharp blade held to your bare heart, and you cannot flinch or cry out. To endure is to let the blade kiss your heart and remain perfectly, defiantly still.
Additional thoughts
The kanji literally stacks blade on top of heart. Visualize a knife pointed downward into a beating heart—the ultimate test of endurance. Ninja (忍者) derives from this very character, reinforcing the image of silent, steely perseverance.
Quick recall
A blade over your heart—hold still, don't flinch, Endure.

Details

The keyword for 忍 is endure. This kanji conveys the idea of bearing hardship, suffering, or difficulty with patience and perseverance. It carries connotations of steeling oneself against pain or adversity, suppressing one's emotions, and quietly tolerating what is unpleasant. The character is also famously associated with the concept of the ninja, whose very name derives from this idea of silent, hidden endurance.
On'yomi
にん
Kun'yomi
しの.ぶ、しの.ばせる

Used in kanji