Throw water on it, maybe
Literally: pleasant – sword – disorder – hemp
Alternately: Skillfully (and quickly) resolving a complicated situation or solving a complicated problem.
Notes: 快刀 is a sword with a good cutting edge; 乱麻 is a tangle of hemp thread or yarn. The yojijukugo can also be expanded to the phrase 快刀、乱麻を断つ (Kaitou, ranma wo tatsu), where 断つ is “to cut (off).”
This compound comes from a story in the Book of Northern Qi (北斉書, in Japanese Hokusei sho), a Tang-era history by Li Baiyao. It’s said that the father of Gao Yang – later Emperor Wenxuan – gave him a tangled ball of yarn to test his intelligence. Instead of trying to work it out the hard way, Yang took the Gordian-knot solution by cutting the tangle apart with his sword.
Replacing either half of this phrase with any homophone, such as 怪刀 (not a common word; literally “strange sword”) or 乱魔 (similarly, “wild demon”), is considered an error.
See also synonym 一刀両断.