Throw water on it, maybe

快刀乱麻
kai.tou.ran.ma

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.

Not the “Ranma” I first thought of; this was the title of a pair of video games, later made into an OVA (Original Video Animation: a direct-to-video animated miniseries).