- Camera data of the DR2 killing game
Nothing implies any data was preserved or even existed in the first place. Just because events are being recorded live doesn't mean they're being saved or stored, and nothing in the game implies such. Considering Danganronpa 2 literally ends with them saying nobody will ever know about what happened, I think it's pretty obvious there's no archives or footage. This isn't even mentioning how Makoto intentionally kept the killing game a secret and even ends Danganronpa 2 saying they're going to cover everything up. Why would any footage exist?
And even if such footage existed, surely future foundation would have gotten it for Makoto's trial, but they didn't. Why? Because it didn't exist. They had to hold a trial specifically because they didn't know what Makoto was doing.
...does not exist in Danganronpa Zero. There is no memory of memory extraction in Danganronpa Zero. The closest I could find was this quote from Yasuke.
"In the future, we might even be able to treat memories like we do data on a hard drive― creating devices to back them up or destroy select parts of them freely. Actually, there’s already research going on for that abroad. By suppressing the enzyme ‘kinase M zeta’, they were able to erase the long-term memory of lab rats."
Firstly, the thing he claims is currently being researched is erasing memories. Obviously, this is something we already know exists in Danganronpa.
Secondly, his comment about some day being able to treat memories like data is not only entirely speculatory, it's also clearly referring to the distant future. Nothing implies this technology ever existed at any point or was ever complete and it's no different from saying "one day we'll have flying cars," and even then it still doesn't make mention of extracting memories.
However, Danganronpa 3 does mention images were taken from the Remnants of Despair to create the AI Chiaki, which is an example of memory extraction, but not from Danganronpa Zero. And even then it's kept vague about how it works, but I'll give you that (though the rest of your argument falls apart later)
3. "...as long as they remain here"
Danganronpa 3 ends with the Remnants of Despair accepting the burden of despair and isolating themselves from the rest of the world. Whether or not you think they stay on Jabberwock Island or they travel the world saving people, they are in no position to ever tell anyone about the events of the killing game, especially since all of them have chosen to move forward from it.
Makoto is speaking from the heart because he knows them. They chose to move forward, and as a result the events of the killing game will forever stay in the past.
4. Makoto's memory could have been extracted in the future or the covering up could be undone
We see footage from the killing game, footage that would absolutely not exist if the events truly happened. We know for a fact that nothing in Danganronpa 3 was recorded, so that footage existing would be outright impossible and make this argument completely fall apart. It's not even footage that could have been extracted from Makoto's memory because the camera is right in front of his face and shows scenes he wasn't even a aprt of.
Even if somehow they managed to "uncover it up," whatever that means, even if they extracted everyone's memories and everyone yapped about what happeend, this footage couldn't possibly exist. Or really any of the footage shown in Danganronpa 53 trailer for that matter.
And all of that brings me back to the original two conclusions, either
- It's all fiction
- It's all a fictional retelling of real events
So TL;DR, it's fiction either way.
Edit: Had to fix some things because I failed to mention a few things