KanjiJLPT N4
Turn

turn, number in a series

Mnemonic

Whose turn is it to guard the grain in the field? Farmers line up in order, each assigned a number. When your turn comes, you stand watch all night, protecting the precious grain from thieves prowling the field.
Additional thoughts
Picture a numbered roster pinned to a fence post at the edge of a moonlit grain field. Each farmer checks the list to see whose turn it is next. The orderly succession of watchmen reinforces the sense of sequential numbering.
Quick recall
Farmers take turns guarding the grain in the field through numbered night watches.

Details

The keyword for 番 is turn. This kanji conveys the idea of taking one's turn in a sequence or order, such as when people alternate in performing a duty or standing watch. It carries the sense of orderly succession, numbering, or ranking, as in assigning a number to indicate one's place in a sequence. By extension, it can also refer to a guard or watchman, someone whose turn it is to keep watch.
On'yomi
ばん
Kun'yomi
つが.い