You find yourself back in the same misty place as when you first arrived in this Lostbelt. That is to say, the afterlife. One has to suppose you succumbed to the fatigue and exertion of the battle against ORT, and finally kicked the bucket. Well, you don't really have any choice but to go meet him.
In one version of Aztec myth, the souls of the dead are divided between those who die natural deaths, and those who die in battle. Those who die in battle are led to the 12th of the 13 heavens, which is the paradise of Teteocan. This place was further divided into four: to the east was Tlahuiztlampa, where those who died in battle and those who were ritually sacrificed went; to the west was Cihuatlampa, where women who died in childbirth went; to the south was Huitzlampa, the realm of radiance, where children went; in the north was Mictlampa, the realm of stillness and rest, where Tezcatlipoca, the god of war and death, ruled. There was also this underworld which existed in nine layers (Mictlan), where those who died were put through trials to become strong and be brought back to the world, where Mictlantecuhtli and Mictecacihuatl, "pure" gods of death, ruled. Most all gods in Aztec myth were associated with death in some form, and it's because of this that Tezcatlipoca is so difficult to understand.
He was the god of war, which means battle was the greatest of all his traits. However, as explained above, the souls of those who died in battle were not led to him, but to the east of Teteocan. Tezcatlipoca might sow the seeds of war, but it is another god who reaps the rewards. Nobody really knows who went to his paradise of stillness, we only really know that his was not an underworld like Mictlan or Xibalba. Perhaps his realm was simply there for those warriors who finally deserved some rest?
You finally find him amidst the fog, where he's seen talking with Daybit. Daybit is saying that Chaldea stopped ORT, meaning Tezca's future wasn't true and he was lying, and liars should be punished, so maybe he should go get Quetzalcoatl from the west, but Tezca begs him not to. They then spot you, and drop the conversation. Daybit says he wasn't sure if you'd come here (it was a 50-50), especially since "this is just a detour anyway", but Tezca was sure of it, since you still have to take back the weapon you pawned to him. If you want to return to being a proper Master, that's what you'll have to do. If this is the boundary between life and death, you'll simply take your Master rights back into the world of the living.
Daybit seems kinda surprised you didn't have your Master rights this whole time, especially since you could summon stuff, so Tezca has to explain that summoning was still possible partly thanks to the Underworld Borders and the established bond with Servants, but you never had the "right" to be a Master regardless. Even when he gave the Command Spells to Camazotz, he kept the Master rights for himself. In other words, you were in a constant state of being nerfed this whole time, which Daybit thinks makes a lot of sense in hindsight.
Well, regardless, you're here, so now you'll fight. Here in Mictlampa, the "payment" you made doesn't matter, and you can fight in perfect form. The winner in this battle will have their payment returned: for you it'll be your Command Spells and Master rights, while for Daybit, he'll be allowed to come back to life and a second chance. More specifically, he'll be taken back to the point where he first summoned Tezcatlipoca. He'd get a second chance at ORT destroying the planet, though of course Chaldea would be there the second time again as well. To redo a whole year, all 516,600 minutes. Well, for Daybit it's only a 30 hour period, so it's more than fine.
You ask why he's so intent on destroying the planet, but he thinks that's a really strange question. After all, you are the same, you and he. It's not about responsibility, but a matter of self-satisfaction. Tezca just laughs at this notion, and then proceeds to declare that whoever wins here will be banished from the afterlife.
Tezcatlipoca
Those who flee, those who dare not kill, and those who doubt their cause. I will never acknowledge such cowards as warriors.
Your hatred of death is excessive. Nevertheless, given how long you've survived on those convictions, I have no choice but to acknowledge you.
Man of Chaldea. If your soul is that of a warrior's, then it is as a warrior I shall respond.
I welcome all warriors.
For the Aztecs, glory is only granted to victorious warriors, something I too endorse. However...
Battles have both winners and losers. The efforts, bravery and determination of the losers are not reflected in such an arrangement.
And that is something I cannot overlook. For those who die in battle ought be rewarded equally.
As such, mine is the realm of the defeated.
It welcomes the souls of those who fought bravely, yet were tragically defeated, destined to be forgotten by all.
These are the ones whose feats I acknowledge, and so I grant them the rest and peace they are worthy of.
So, which one will it be, Fujimaru?
Will you lose, pass over to the paradise beyond the horizon, and so earn your rest?
Or will you win, and return to your battle once more.
Win here, and the seventh Lostbelt officially ends, alongside Nahui Olin, the Fifth Sun. This is the ultimate time to show your resolve and choose between life and death. However, Daybit says your choice does not matter, only your actions. He is certain he will win here.
Daybit
Chaldea's excessive abuse of the Human Order won't be good enough against the Alien God.
CHALDEAS---no, Marisbury is not an enemy of mankind.
Marisbury is an enemy of the universe. And if I'm the only one who could manage to see that---
Then by destroying the planet, I will make sure that the bad name that would befall humanity never happens.
You would save the world. I will save the universe.
Even if our objective of saving mankind is the same, as long as our methods are different, we will have to confront each other.
Ready yourself, Fujimaru. Neither of us has a handicap now.
I hereby challenge you to battle not as a Crypter, but as a Master.
Besides, this will be the last time. Let us see how it'll be to carry out the battle I simulated so many times in that Coffin.
Daybit (battle start)
Where there are no deaths, no births, and no cycles, there is nothing securing the Human Order, and a god lies in the void. Its name is CHALDEAS. Alien God CHALDEAS.
(During this fight, Daybit uses his 3 Command Spells (since I guess he has them all again here) to buff Tezca at each break bar, as per usual for boss fights, but once you "kill" Tezca in this battle, it does not end. Instead, he revives to full HP, proceeds to fully charge his own NP, and the NP of your entire frontline, while locking your non-NP cards. At this point, you have a single turn to wipe him out with your (up to) three NPs, else he will retaliate with his own and end your stay in Mictlampa. There are no revives here. You must win.)
As expected, when fighting as Masters, then you are the victor. Well, Daybit thinks it's a bit weird he didn't get any other Servants other than Tezcatlipoca, since you'd at least think an almighty god would have some "followers" to make use of, but whatever. What's lost is lost, and the outcome is perfectly clear. As he's about to leave, you stop him and ask if ORT was really the only way he could have fought the Alien God.
Daybit
...It was. I'm not able to build up trust with others like you are.
After I joined the A-Team and understood the truth behind CHALDEAS, it was already too late.
The completed CHALDEAS is a planet unto itself. Nobody can destroy it.
I tried to threaten Marisbury into stopping his plan, but he took his own life instead.
All he said was: "My life or the Securing of the Human Order---which one should I protect? What a silly question."
At that moment, I had no choice but to play along with his plan. If I wanted to be able to destroy CHALDEAS, I couldn't do it as an outsider.
My prediction was that the chance to destroy it would only befall those who stayed part of Chaldea until the end.
In other words, you people. I chose to remain as a Crypter, but---
Who could've thought that a new Chaldea would fight against the old Chaldea?
Novum Chaldea, was it? Not a bad name.
He begins walking away, and once more you try to stop him, but Tezcatlipoca tells you to let him be. At this point you're robbing the loser of even their right to exit the stage, and he will not allow that here. You should just see him off. In this moment, there is no one more worthy of Mictlampa than Daybit. Well, he tells you not to worry. This place is like a spa of dreams, but it's not eternal. Once Daybit's rested, he'll be sent right back into battle, and then he'll actually be on the winner's side, he says. This place is just a pit stop, one to prepare you for the next battle.
Tezca returns your Master rights, and says it's a good thing you weren't partnered this time around. He's a god who picks everyone's side in battle, but this time he specifically chose Daybit because of the scope of his destruction. As a god who'd seen so many countries be destroyed, a planet being the target was definitely exciting. Still, he says, there are no battles in which everything is destroyed. You might have ended Mictlan, but you certainly didn't destroy it. Extinction is a common occurrence in Aztec myth, but so is the fact that something comes back afterwards. Even if everything ends, something lives on that can never be destroyed: time.
Tezcatlipoca
That "something greater" the Deinos were talking about.
Yeah, that's correct, boy. What the Deinos served was time.
If the Deinos come over to my paradise, this is what I'll say to 'em: "You guys had one hell of a friend."
I know you people like to think of time as something you measure. That it accumulates. That it's got significance just 'cause of that.
But even if you or your countries are destroyed, time will never disappear.
Humans usually have this idea that they're passengers through time.
But actually, time's the passenger, and humans are kinda like a river that carries it forth.
You better put this to memory, Fujimaru. Humans aren't the only ones who whittle away at time.
There's the time observed by humanity. The time recorded by machines.
The time that wears away at matter. The time that cools down the planet.
So long as they're all still around, our world's indestructible.
It has no end. Even if things disappear, and even if this planet loses its purpose...
Time will always keep on going toward the future.