Note. To the best of my knowledge this is not based on any existing Fallout Equestria storyline, nor does it follow any particular plot in Fallout 4. This is just the narrative that popped into my head as I worked on this piece. This is a Patreon patron reward for .

The doors to the classified research laboratory hissed open allowing a light mauve alicorn mare to enter the room. The room was unoccupied with the exception of the specimen floating in the growth tank. Twilight Sparkle slowly checked various status screens and daily condition reports. The progress looked good but she knew not to get her hopes up. They'd been dashed too many times already.
Having reviewed the updates she slowly walked toward the center of the dimly lit room. In the center was large, clear, fluid-filled cylindrical chamber about 12ft tall. Floating naked inside was a body. A large pale alicorn with a long, flowing, multi-color mane and tail. Her face was obscured by a respirator and VR headset that covered the alicorns eyes. Deeply implanted earplugs isolated the mare from outside influences. Various hoses and cables and intravenous feeds were connected to the floating subject. The figure was still except for an occasional twitch or movement of the head.
Twilight slowly walked around the cylinder several times examining the specimen's growth. From a nearby table she retrieved a clipboard and reviewed the day's evaluation from the research staff. Returning to the cylinder she noted that the staff was correct that based on historical data the cutie mark on the specimen had several discrepancies from the original mark on the princess. However it was still an important milestone that the specimen had grown one at all. Only 4 of the last 26 attempts had gotten one at all.
Twilight reached out and gently touched the side of the cylinder making sure to no disturb the occupant inside. So much was riding on this project. Too many Institute resources had been committed for this to fail. Too much was riding on this. The Institute had gone to great lengths to mount an expedition to the ruins of Canterlot to obtain the necessary biological samples to make this project even feasible. Too many in that expedition paid the ultimate price to fail now.
Besides the other project had ended up being a disaster. Not only had the it failed to recreate the Princess of the Moon it had instead had succeeded in producing what seemed to be a very violent, version of the alicorn. It had then attacked the staff before escaping to the surface world leaving a wake of death and destruction. Fortunately that corrupted version only appeared to have limited lunar control, but it had succeeded in starting a cult on the surface and was amassing followers.
The specimen's head suddenly started moving slowly from side to side, and it began making small gestures with its arms. Twilight glanced down at the clipboard. The specimen's movements appeared to its reaction to sensory input from a recording of a Hearth's Warming Eve festival that had been recorded a few years before the war.
Based on the failure of Project Luna the Institute was doing a much more extensive conditioning regime for this synth. Great effort had been made to retrieve from various archives every bit of information available on the late Princess Celestia to give them the best chance of reconstructing her personality.
This was the Institute's great gamble. A calculated gamble, but still a gamble. The Institute's was hoping the synth Celestia would grant them access to the great power of the sun which they could use to embark on greater expansion of their facilities. Also history had shown that the Princess of the Sun was probably the most beloved pony ever. The Institute hoped that the resurrected form of her would make her an ideal ambassador to the surface, and would help them secure the necessary cooperation of the surface dwellers for several large above ground projects. No matter how distasteful they were, it would be easier to get the desired results with them on their side.
Twilight shook her head. But that wouldn't happen if her team failed to create a viable specimen. Glancing over at the clock on the wall she realized it was well past her bedtime. She took one last look at figure in the cylinder and then wandered out of the room.

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