expression
come hell or high water; no matter what happens
Idiomatic expression conveying unwavering determination regardless of any obstacles. The literal image is 'even if rain or spears should fall'.
See also: 雨が降ろうが槍が降ろうが
雨が降ろうと槍が降ろうと、明日の試合には必ず出る。
Come hell or high water, I'll definitely participate in tomorrow's match.
彼は雨が降ろうと槍が降ろうと、約束を守る男だ。
He's a man who keeps his promises no matter what happens.
A set phrase combining 雨 (rain) and 槍 (spear) with the volitional form 降ろう (fall) and the particle と (even if). The exact origin is uncertain, but it likely emerged as a dramatic way to express determination against any adversity.