KanjiJLPT N4
Case

affair, case, matter, item

Mnemonic

Butler Alfred opens a strange case: a cow has wandered into the grand hall, chewing on the curtains. Alfred calmly approaches the cow, clips a case number to its ear tag, and begins filing the incident report with perfect composure.
Additional thoughts
Picture Alfred standing beside a huge cow in a pristine ballroom, clipboard in hand, utterly unfazed. A person (butler) + cow = a case to handle. The ear-tag case number reinforces the counting/incident meaning.
Quick recall
Butler Alfred clips a case number onto a cow that wandered into the manor.

Details

The keyword for 件 is case. This kanji refers to a matter, affair, or individual instance of something that needs to be addressed or considered. It is commonly used when counting or referring to specific incidents, events, or items of business. Think of it as identifying a particular case or matter among many, much like how one would file individual cases in a legal or administrative context.
On'yomi
けん
Kun'yomi
くだん