KanjiJLPT N3
Stature

stature, height, back, behind, disobey, defy, go back on, rebel

Mnemonic

Heading north under a full moon, you see your shadow cast behind you on the snow. It stretches enormously, exaggerating your full stature. The low moon in the north sky makes everyone's stature look gigantic — shadows towering across the frozen landscape.
Additional thoughts
The North Pole's low-angle moonlight elongates your back-shadow, naturally linking the back of the body to height. Picture yourself standing tall, spine straight, your stature measured by that impossibly long silhouette on arctic snow.
Quick recall
Your shadow under the north moon exaggerates your stature across the snow.

Details

The keyword for 背 is stature. This kanji refers to one's height or physical build, particularly the measurement of a person's back from top to bottom. It also carries the meaning of the back of the body itself, and by extension can imply turning one's back on something, suggesting rejection or defiance. The connection between the back and stature is natural, as a person's height is often assessed by looking at the length of their back while standing upright.
On'yomi
はい
Kun'yomi
せ、せい、そむ.く、そむ.ける