During the creation of the Lockseeds, a failsafe was included within them, which can be mentally triggered when transformed and utilizing said Seed. If the user is in danger, they can release all of the Seed's power in one destructive burst, but it drains the Seed of all power.
When a Seed uses a finishing attack, the Seed will replenish energy over time. When this is used? The Seed turns black and is now considered "rotten". If the user keeps fighting with a Rotten Seed, the armor will turn black, and their Arms Weapon will now be black and brittle, capable of breaking in a few blows.
A downside to using a Rotten Arms is that it will actually damage the body, and start draining energy from the user in order to compensate for its lack of power. This energy is usually in the form of life-force.