expression
through thick and thin; through fire and water; hell and high water
Idiomatic expression meaning to go through any hardship or danger for someone or something. Often used in the pattern 〜も厭わない (won't hesitate even through fire and water).
彼のためなら火の中水の中だ。
I'd go through fire and water for him.
火の中水の中、どんな困難も乗り越えてきた。
We've overcome every hardship, through thick and thin.