"Sloppy. Would have been cleaner to level the entire thing. But then I suppose it might have been harder to pretend it was a war."

"Cleaner to ... excuse me?"

"Total destruction. Rather than this..." she gestures. "Haphazard effort."

"... have you seen a massacre like this before?"

"The Empire I come from fights on a scale of worlds. I have, in fact, caused massacres like this before. When I was younger and slightly more foolish."

And he taught her alchemy. At least most of the theory that would allow her to construct new arrays has been focused on healing. Of course, knowledge of the human body can be its own weapon.

"I see."

"I have no interest in doing so again without good cause, if that helps to ease your mind."

"I --" he pauses and continues miserably. "I have no room to judge. I was complicit in Homunculus's plan, all those years ago, which involved much the same thing."

"If only the innocent were permitted to judge, no one would ever be called to account."

"True."

They come to a giant wall. It's about two meters thick and twenty tall.

"What's this, then?"

"The edge of the area. The bases for the extermination campaign."

"Crude, but effective. Do you already have a way through?"

"The composition is consistent enough that it takes very little alchemical knowledge to make an appropriate-sized hole and close it afterwards."

He shows her, detailing the types of rocks that make up the wall, and the likely elements and their proportions.

And with that, she can draw up the array and activate it.

It works! Hohenheim is pleased.

After they go through he shows her the changes she needs to make to the array to seal it behind them. "You'll notice rectangular cells that stick out from the area you transmuted. Ideally a transmutation will omit those, especially for detailed work. But this wall has plenty of them all over the surface, so a few more won't be missed."

"What causes those?"

"Usually it happens when the proportions of the materials you're working with are slightly off from what you predicted, but your array is otherwise sound."

"Difficult to eliminate entirely, then."

"Yes, unless you prepare the materials beforehand."

"I see." Modifications complete, she seals the tunnel.

The desert turns into rocky steppe. Hohenheim relaxes when they start to see green grass. "We're close, but it's getting late. We should camp here."

"Very well." They can set camp.

"I sense some reluctance within you."

"I haven't seen my wife in years," he says. "I ..." he trails off and goes silent.

Occlus waits patiently.