The White Demon of Chaldea (Error 404 in Fate/Grand Order)

Prologue

Thanks to Azi for helping me think of how to do an Alphaverse x Nasuverse story

==Chapter Start==

It was painful. Error 404 was barely alive for now, but he could feel everything start to get fuzzy, code scattering from his body and going somewhere else. He was dying. He was the sacrifice needed to do the Error 666 transformation, and using the Butterfly transformation when the Mainframe was weakened meant he wouldn't return. Not this time.

But he was okay with that. As long as Error was okay...he would be fine, as much as it would hurt to leave Chara and Adam again...

He could feel Error trying desperately to keep the transformation up, anything to make sure his father wouldn't die. 404 could only shed a tear at being thought of as one...it felt nice. Too nice for him to deserve.

It would hurt to leave his son.

404: 'I'm sorry Error. I'm sorry I'm going to have to leave you like this, but at least I know that you are okay. And...thank you. I know that I can be a pain to handle, and we fought for so long...but you stuck by me, and I realized now more than ever...that I'm happy. I feel happy when I teach you and help you grow. So thank you...son, for making this old bastard feel again...'

As he felt himself fade away, Error 666 starting to disappear, something happened.

The Mainframe, the life source of reality wouldn't allow this. It wouldn't allow Error 404 to die. It recognized 404 as a part of itself, and if he was dying, it would die too, or at least that is what it concluded with. It needed to do something for its survival.

So as Error was left holding 404's jacket, a black goo crawling up through his leg, the Mainframe had taken him. Or at least, 404's code. His code was precious, basically a part of the Mainframe. The code was then split, leaving two pieces. One larger than the other. The Mainframe then stored the smaller piece inside of a seed that had appeared inside of where 404's HQ is, where the Mainframe pool was before planting it.

It would be a backup, sort of like a file in case anything goes wrong where it then can then take the fragment that would grow and cut off the dying piece in the event it does not recover or something else endangered the Mainframe again.

So what would it do to the bigger part? Leave it somewhere where it could recover. So it searched the lower dimensions, alternate dimensions, any area in which it would be able to safely recover in its weakened state.

But it was...troublesome. This reality and the surrounding ones were dangerous. Very dangerous. And with the weakened state of the code it currently had, it would need an area where little threats to its being would exist...

So it consulted to a higher existence. A higher being. Something to help keep it alive. And so that higher being answered.

There.

Nasuverse. While dangerous, more so than the realities around it currently, it wouldn't be much of a problem. The area wasn't strong, only a certain few sections. And even then, they almost never interfered. Just existed as a heart for the dimension or as a protective barrier if something harmful tried to enter it.

But there was something special. The Throne of Heroes. While the body would stay, the soul would be traversing through the infinite universe and timelines to learn. The perfect environment for the weakened code to heal.

Sure, a completely different system, but it trusted the code to adapt.

So it trusted the code to the higher being. The higher being grabbed the code and started to traverse through the infinite dimensions and stories that lay inside existence. One far away from the "fandom" of "Alphaverse."