The Demon Armor is a central plot element of Devilman Saga. It is a unique armor that contains the souls and memories of demons.
The Demon Armor is made of a unique type of matter that cannot be understood with most material testing, making it a higher dimensional state that is not easily understood. If ever broken or damaged, the armor is capable of repairing itself unless the pieces are either too far separated or in a cold environment. Inside the armor are a series of sharp spikes, something that would prevent a regular person from wearing it. However, once the armor breaks down and bonds with the host, it can be worn in a number of size and shapes after piercing and merging with every cell in the host's body.
It is apparent that the armor contains the souls and memories of its users both past and present. The armor seeks out wearers by guiding them towards the suits or forcibly attaching itself to them, bonding with hosts of their choosing. Depending on the demon inhabiting the suit and the wearer, one or both sides can dominate the other in a manner similar to how Demons possess their hosts. Most armors prefer to be in a complete state before bonding with a host, but in times of great stress or emotion, the armor can bond with the host in an incomplete state as it did with Yuki Fudo.
The armor communicates with hosts via a telepathic link that only becomes complete when fully bonded. This is shown as a type of landscape that exists between the consciousness stored in the armor and the current wearer, allowing communication between them. However, most hosts that do not possess a strong will or are in a state of weakness are easily overwhelmed becoming overtaken by the demon. Those that don't however can either overpower the demon's consciousness or work with them for a shared goal.
Once fully bonded, the armor allows the wearer to possess numerous powers depending on the armor. Common abilities include enhanced strength, speed, agility, senses, and reflexes that vary. Other abilities include flight and releasing energy. The armor can also combine with other armors into a stronger form.
As the armor bonds with the host on a cellular level, the host slowly goes through mutations that change their anatomy into a different form, often based on a previous wielder.