tim!

Mnestic Experience seems to focus on the concept of Taboos and the violation thereof; the main image for it indicates it's going to center around Kim and Aeng-du (S Corp fugitives), Ezra and Meursault (N Corp fugitives), Yi Sang (T Corp fugitive), and... Faust. As such, Faust has likely violated some Taboo or other in the past.

MOTWE has Faust imply that she is under constant surveillance and has her every action scrutinized and controlled; while this could refer to the Gesellschaft, they seem to care a lot less about actions and more about knowledge and results - whether she does or doesn't collect the Boughs. As such, it's possible that Faust is also being surveilled by a third party.

Faust's characterization and appearance both draw heavily from Angela, an AI who by her very nature violates the laws of the Head; the Head's Beholders also seem likely to be one of the few factions of the City capable of placing someone under perpetual surveillance, and we see in LoR that they're willing to let certain Taboos slide so long as the person who violates them has the potential to un-violate them, with Angela being allowed to live in the City so long as she's on the path to obtaining the One True Book and transforming into a human.

In the latter half of Goethe's Faust, Faust dedicates himself to the project of creating a new country by pushing back the sea and creating more space for humanity to live. In the world of Limbus Company, this would likely translate to something like Faust pushing out the City's borders into the Outskirts, something that the Head as a pro-human faction would likely be extremely interested in the success of, explaining why they might then tolerate the continued existence of someone who has violated a Taboo.

"Mother used to say that however miserable one is, there’s always something to be thankful for. And each morning, when the sky brightened and light began to flood my cell, I agreed with her."