expression
couldn't kill (someone) if you tried; tough as nails
A hyperbolic set phrase meaning someone is so tough or resilient that even an attempt to kill them would fail. Often used figuratively about a person's tenacity or indestructible nature.
あの人は殺しても死なないタイプだ。
That person is the type you couldn't kill if you tried.
殺しても死なないような強さを持っている。
He has a toughness as if you couldn't kill him if you tried.