#i could be off base here but parts of this are definitely true

[prettycottonmouthlamia]

So the S-stages for Babel don't share the same convention as the normal and EX stages. They're not a call and response between Theresa and Theresis. Instead, they're "Simulated Assassinations" and their description is about the construction of a simulation.

>Simulation building complete. We will stop the assassins in the city this time.

The description for BB-S-4, "Simulated Assassination 4". Given the name of the stages, this is seemingly involving some kind of simulation regarding Theresa's assassination. Someone is running a simulation to see if they could have stopped the assassins from leaving Kazdel.

This is further supported by the number of Assassins on this stage.

There are 13 Deathveil Assassins on S-4, and boy do you feel it. Never want to deal with this many of these bastards again. But this isn't the only stage with 13 Assassins.

BB-9 also has 13 Assassins on it, so the connection at least to me is pretty clear. Your goal, on this map, is to stop the assassination of Theresa by stopping the assassins in the city.

It is worth at the moment to discuss the diegetics of the battle screen for a moment. When you're in a map, that is a simulation of a battlefield that is present in the Doctor's mind, the source of his ability to be precise and calculating in a tactical role. But there are moments where this diegesis is broken. BB-10, for instance, is a reversal of this outcome, where Theresa is in the Doctor's mind and the simulation is a battle in the Doctor's head. In addition, there is the matter of PRTS's involvement, and this means that it's potentially likely that these simulations can be done on PRTS's side as well.

Which means that the narrative of this stage, is that someone is running a simulation to prevent Theresa's assassination. Given the epithet of these stages "You the Constant, You are Me" this points to the only two "constants" on Terra: the Doctor, and Kal'tsit, and I can think of someone who wracked with guilt would do simulations to prove that it should have been possible to stop her death.