Which allies fight alongside Fei here (the outline asks: Shevat? Bart?)
Shevat and Nisan are ineffective against the giant Mobile Surface Supremacy Weapon.
Fei and his allies (Shevat? Bart?) push back Solarian Gear units, then head for Kislev's capital to retrieve the administrative structure and activate Yggdrasil IV.
Solaris facilities ("these facilities existed all over the earth", therefore the first big one must be in a populated part of the world), no specific one location in the world map.
Full of civilians (human and demi-human), Wels mutants devour the natural ones and later lesser-mutated ones.
Some Wels are hostile (like the cages in Krelian's Lab), we can assume enemies would be primarily rebalanced Wels and Kislev/Etrenank mutants.
The party is Fei, Citan, and Elly (can be changed, therefore all party is accessible).
Gebler officers confront Elly about her being a "have" when they're "have-nots".
Final encounter is the Sufal Mass.
Later comment about how there are mutated human-Gears like Hammer present here.
The party go "from place to place, destroying all the Soylent System facilities"
Nisan provides shelter for the mutated victims of Krelian's virus, offering treatment.
Those who had mutated only mildly were treated with Taura's nanomachines, which reconstructed and revived them.
Unfortunately, there were some that had such accelerated symptoms that their treatment was not as promising... Trying to bring them back to a form that resembled a human was the best that could be done.
The mutants no longer fought each other as they did in the Soylent System.
Elly is hailed as the reincarnation of Sophia, the woman who founded Nisan.
The Gazel Ministry comment on the people gathering in Nisan and how it might benefit them.
They seek to activate the Goetia Key, but Cain stops them.
Gameplay expansions
Where, why
Mass-Driver dungeon. Crucial to the story and very detailed in the narration. Only 2 other Zeboim areas in the game. Existing project: https://www.youtube.com/watch?v=9HEEY3u8RgQ
Soylent System dungeon. One of many but very detailed in the game’s files and therefore can be rebuilt easily. Sufal Mass is already a boss in the final part of this dungeon. Existing project: https://www.youtube.com/watch?v=dikKCWbQW18
Overworld exploration. Finding the Mass-Driver (walking from Taura’s House should be very simple. This could be applied to chapter 51 too, then). Soylent System is trickier because it doesn’t exist on the world map, but could require the player to fly with the Yggdrasil.
Lighthouse. Coinciding with Mass-Driver, the area could be made accessible starting this point and for throughout the rest of the disc.
Why not
If recreating the dungeons proves too troublesome. Canon conflict should not be an issue, as the dungeons seem to have been intended to be playable originally.
Overworld should require minimal tweaking besides NPCs reacting to Etrenank’s destruction (only text).