KanjiJLPT N1
Nest

nest, rookery, hive, cobweb, den

Mnemonic

A bird plucks hair from a sleeping dog, strand by strand, then weaves it all around a plump fruit still hanging on a branch. Layer after layer, the hair wraps the fruit until a perfect little nest takes shape—round like the fruit, soft like the hair inside.
Additional thoughts
Picture the round fruit as the bowl-shaped frame of the nest, with animal hair woven around it for insulation. The fruit gives structure; the hair gives warmth.
Quick recall
Hair woven around a fruit on a branch forms a cozy nest.

Details

The keyword for 巣 is nest. This kanji refers to a nest or dwelling place built by birds, insects, or other animals, such as a bird's nest in a tree or a beehive. By extension, it can also refer to a den or hideout used by people, particularly in the sense of a base of operations. The character conveys the idea of a constructed home or shelter within a natural environment.
On'yomi
そう
Kun'yomi
す、す.くう

Used in vocab