The antonyms for the phrase "remains firm" would be "becomes weak", "loses strength", or "wavers". These terms convey a sense of instability or uncertainty, indicating that something is not steadfast or resolute. When something "becomes weak", it is more easily swayed or influenced; when something "loses strength", it is less capable of withstanding pressure or challenge; and when something "wavers", it is uncertain or indecisive. These are all opposite qualities to those associated with something that "remains firm", which implies strength, stability, and a steadfast commitment to a particular course of action or belief.