Calamity

"The one that you call "Seido" is no more. We are Calamity – the Cosmic Destroyer."

- "Calamity".

Seido, now known as Calamity was a Cosmic Protector.

Cosmic Protector
Long ago, in the Flagnoverse, there was a being who always defended it. He was appointed to protect that reality be the One Being themself. This being was Seido, the Cosmic Protector. He protected the Flagnoverse for the many eons he was a Cosmic Protector.

One day, the Keepers of Reality held a meeting with the Cosmic Protectors of every reality. The Keepers told about a dimension-hopping beast that wreaks havoc wherever it goes. The creature goes to a reality, ruins it, and continues the cycle. They do this by slowing time to a screeching halt and wreak havoc with zero consequence. This creature was known as "Kas Tai." The creature has even evaded the other Cosmic Protectors. The One Being said that the Flagnoverse was next on Kas Tai's list. Seido was told to kill the monster.

Eventually, Kas Tai arrived. Kas Tai stopped time, but Seido was prepared. Seido struck a fatal blow from behind. Or at least, it should have been fatal. Kas Tai simply hit Seido back. The two then clashed with all their might. Seido was too focused on defeating Kas Tai to pay much thought to time returning to normal. It was a long battle, but Seido came out victorious. Seido then punched his hand through the creature’s chest and began to absorb it. The last thing Kas Tai did was howl in agony for four seconds until its body was completely absorbed. Seido was never the same after that.

Seido would learn that Kas Tai was very close to having the power of the Ultimate Element. Seido kept feeling strange. He felt weaker, he became paranoid, something completely unlike a Cosmic Protector. The Keepers of Reality and Cosmic Protectors of other realities became rightfully concerned. Seido kept telling the others that he was fine, which everyone knew was not the case. Seido said that he did not need help, nor did he want it. One day, everything went wrong.

Kas Tai was gone, but he did not leave. The beast was still alive in Seido's mind, corrupting it. The beast was gaining control over Seido's mind and body. Seido was quite literally fighting the ultimate battle within him. This time however, Kas Tai won. Kas Tai intended on absorbing Seido into himself, a fitting end as he thought, but ended up assimilating themselves into a horrifying beast with unfathomable power.

Seido's appearance underwent a drastic change. His armor became darker, more menacing. His mask changed from looking heroic to sinister. Even his voice changed, becoming deeper and more hostile sounding. Seido was now two beings fused into one. They abandoned the name "Seido" and "Kas Tai" and called themselves "Calamity".

Calamity
Calamity now set out to finish Kas Tai's work: wreaking havoc on all realities. This time, armed with the powers of a Cosmic Protector, Calamity could now end realities, which was exactly what he did. No reality was safe from Calamity. Calamity ended some realities outright, but saw little fun in that. Calamity then warped realities, reworking those realities' laws of fundamental physics. Every Cosmic Protector was able to undo Calamity's work, much to his displeasure.

Calamity set his sights on a reality he has not been to yet: the Negaverse. The Keepers of Reality could see this and warned the Cosmic Protector of that reality: Meltdown. Meltdown said that he had a plan, but would most likely take the combined efforts of every Cosmic Protector and Keeper of Reality.

Soon enough, Calamity came to the Negaverse. There, Meltdown put his plan into action. Calamity was struck blow after blow. He could not land a single hit on any of the others. Then, every Cosmic Protector and Keeper of Reality unleashed a beam that obliterated Calamity. Calamity was now gone. Now the Keepers of Reality had to find a new Cosmic Protector for the Flagnoverse.

Abilities and Traits
As a Cosmic Protector, Seido possessed great patience and intelligence. He was dignified and had a strong sense of conviction. However, once he absorbed Kas Tai, Seido slowly descended into madness. Kas Tai's mind was dominant when Seido was Calamity.

As a Cosmic Protector, Seido had the Ultimate Element, meaning he was capable of literally anything. Kas Tai was very close to gaining access to the Ultimate Element. When Seido absorbed Kas Tai, he finally had access to the Ultimate Element. After being fused, Calamity now called himself the "Cosmic Destroyer".

Mask and Tools
Seido wore the Kanohi Orden - the Mask of Harmony. With that and his powers, he made sure the universe was in balance. Everything was as it should have been. Until of course Kas Tai came along. After being fused, Calamity wore the Kanohi Condenar - the Mask of Armageddon. With that and his and Kas Tai's powers, he destroyed reality after reality.

Seido wielded a Red Sun Staff. The top of the staff was an actual red sun. Seido thought it was a good choice of a tool. With that, he could shine light in the darkest reaches of space, unleash jets of fire and fire small "suns". As Calamity, the staff gained a more sinister look. He named it his Staff of Armageddon. He used that to destroy suns in solar systems, unleashing supernovas that annihilated those solar systems.

Trivia

 * The name Seido comes from the alternative name of Orderrealm from the Mortal Kombat franchise.
 * seidō (制度) is Japanese for system or organization.
 * His other name "Calamity" comes from the High Epic of the same name from the Reckoners series.
 * Kas Tai is Lithuanian for what is it?.
 * Orden and Condenar are Spanish for order and doom respectively.
 * Originally, Calamity was supposed to be imprisoned in stone and left in Chevas's castle in Furnace.