KanjiJLPT N2
Boil

seethe, boil, ferment, uproar, breed

Mnemonic

A violent storm rages, knocking out all power. You desperately need to boil water to survive. In a panic, you grab a hundred dollar bill and set it ablaze as kindling beneath your pot. The water finally begins to boil just as the storm howls even louder outside.
Additional thoughts
Picture the absurdity: burning precious cash because the storm killed the stove. The desperation reinforces the intense, seething energy of boiling. Storm = water context, hundred dollar bill = the extreme fuel.
Quick recall
A storm kills the power, so you burn a hundred dollar bill to boil water.

Details

The keyword for 沸 is boil. This kanji refers to the vigorous bubbling action of liquid being heated to its boiling point, where water reaches the temperature at which it rapidly turns to steam. It conveys the sense of something seething, churning, or reaching a state of intense agitation. By extension, it can also describe emotions or situations that are figuratively boiling over with excitement or turmoil.
On'yomi
ふつ
Kun'yomi
わ.く、わ.かす