|This article is about a/an organization in Kamen Rider Build.|
Downfall is the terrorist organization with the goal of defeating the Kamen Riders in the New World with the leader, Simon Marcus become the ruler of it. Their members can transform into Phantom Crushers, created by Keiji Uraga from the new formula namely Phantom Liquid. Their abilities upon transforming into Phantom Crushers are negating the transformation of the Kamen Rider which is created from Nebula gas. However a part of the group would initially be beaten by Kamen Rider Grease and the Hokuto Sanbagarasu as Kazumi and his co unknowingly to have found the source of the Phantom Liquid in the form of a pool of hotspring on an unknown island and taken a bath on it.
They are responsible in abducting Misora Isurugi as Keiji doesn't know the fact that Misora's manipulation of the Kamen Riders' power is coming from Vernage, and Vernage is no longer exist within Misora which resulting the abduction is nothing but a futile work. Despite that, Keiji used Misora as a bait for Grease to have him gave the White Pandora Panel so Keiji could use it to manipulate the world as he wished after he killed Simon Marcus.
The group reached their ultimate downfall by all Build Riders after Sento found a way to replenish their power.
- Keiji Uraga - true leader (Kamen Rider Metal Build, killed by Kazumi)
- Simon Marcus - former leader (Phantom Crusher, killed by Keiji)
- Several members (Phantom Crushers, killed by Hokuto Three Crows, Build Genius, Cross-Z Magma, Prime Rogue, and MadRogue)
- Guardians (hacked, destroyed by Cross-Z Magma, Rogue, MadRogue and Grease Blizzard)
- Hard Guardians (hacked, destroyed by Grease Blizzard)
- Downfall is notable as a villainous organization in that many of its members are not of Japanese descent.