KanjiJLPT N4
Crowded

crowded, mixture, in bulk, included, (kokuji)

Mnemonic

A path becomes crowded when too many people try to enter it at once. Imagine a narrow alley where hundreds surge forward — bodies packed so tight you're lifted off your feet. The more who enter the path, the worse it gets, until no one can move at all.
Additional thoughts
Think of a subway entrance at rush hour: the path down the stairs is jammed because everyone is trying to enter simultaneously. Path + Enter = Crowded.
Quick recall
Too many enter one path — it gets crowded.

Details

The keyword for 込 is crowded. This kanji conveys the sense of things being packed in, entering into, or being jammed together in a confined space. It carries the fundamental idea of going into or putting something inside, which naturally extends to the feeling of being crowded or stuffed full. The character is widely used in compound verbs to express the nuance of doing something thoroughly, deeply, or inwardly.
Kun'yomi
-こ.む、こ.む、こ.み、-こ.み、こ.める