"Why… why didn't you tell me before?"
"I misjudged the effect that it had. I thought it was a strength/stealth artifact set at first, but apparently, the stealth effect comes from one of the hourglasses. Also… I had hoped that we would not come to this…"
"You mean…?"
Beidou went quiet for a while. She unsummoned her sword and extended her hand to the sitting Sai, making sure to dodge the artifacts.
He took her hand, and she pulled him up and into her embrace. Suddenly being hugged, Sai didn't know what to do.
"B-Beidou?"
"Sai, you must stay strong."
"What do you-"
"There's only one way to save you." She paused while he… froze. "I will teleport away from here, then I will immediately go get my whole crew to excavate this entire hill. You must stay here, waiting for me. Don't try to enter the domain on your own, and don't do anything rash. Just conserve your energy. I might take a few days, but I promise I'll save you. I promise you!"
The grief in her tone told Sai that she was dead serious.
"I'll bring you Osmanthus wine and plenty of awesome snacks with me, so can you do that? Can you wait for me here?"
"I… I…"
A lot went through Sai's mind at that moment. All this suffering, starvation, resilience… All for naught. Now that he was free from the effects of the Brave Heart and whatever other artifacts they got, Sai could think things through with confidence. Therefore, he knew how unrealistic Beidou's plans were.
Supposing that she teleported at the closest Waypoint, which was already unlikely, it would take at least several hours for her to reach her crew. Of course, that's if she wasn't attacked on the way there.
Again, supposing her crew was where she thought they would be, she would need to get some rest herself, and then drag a whole retinue to the Fatui camp. Assuming she'd quickly defeat them and that there were no strong reinforcements… If she somehow managed to do all that in half a day, that's when they would start digging.
But even with thirty people digging non-stop, it was unknown how long it would take for them to find the domain doors, if they could find it at all. He didn't think that Beidou could accurately remember the turns they took inside of the tunnel, so there was a lot of margin of error for the location they looked for. And worse yet, they didn't know how deep it was.
In summary, if Sai used all the luck accumulated in his lifetime, she would manage to get him out in at least a whole day. It would be the third day in a row that he was terribly malnourished. Although that wouldn't kill him, it was still akin to hell, one that got continually worse.
And that's for the best alternative. On a realistic approach, she would take at least a week to retrieve him. Sai didn't know if he could survive without water for that long.
"If you could teleport, why didn't you go already?" He asked calmly.
The truth was that she couldn't before, as the domain doors blocked her connection to the Teleportation Waypoints. But she would rather kill herself than to allow a single shroud of doubt to grow on the boy's heart;
"I hoped that we could escape together by getting through the domain… But I was wrong."
They both remained in silence for a while, each with their own worries. When Beidou was about to ask him again, Sai reached a conclusion.
"Go. I'll stay right here waiting for you."
It would be foolish to force her to stay with him and try other alternatives, especially when he knew that this was the best option he had. Regardless of what they did, Sai depended on her to get out. He was too weak to be of any help, so he at least tried to not burden her too much emotionally. By doing this, he would feel better with himself.
Beidou smiled weakly. Sai continued:
"If you perchance don't find me on time… Don't blame yourself, okay? This wasn't your fault. Please, promise me that you won't blame yourself."
"I… I promise I'll try."
"That's good enough. Now go!" With that, Sai pushed her lightly.
Beidou looked at him in the eyes, gritted her teeth and repeated with determination:
"I promise I'll make it on time!"
The pirate then raised her right hand and made a squishing motion. Purple light surrounded her, and when Sai looked ahead again, she was gone.