i had an idea for a spinoff that would have taken place in between ME1 and ME2 that i briefly looked into developing into a tabletop RPG when i happened across a handbook for ME tabtletop RPGS that someone adapted from the Star Wars handbook. i think the plot, or something like it, would make for an interesting movie or streaming series too. *spoilers for ME1 and 2*:
it would open with a scene of a busy transit hub on a seedy Terminus Systems planet, featuring the voiceover of a news report about a private medical research tech company's breakthrough in developing Synthetic Eezo, and then close in the fiery wreck of a ship careening out of the sky and crash landing. a local security official is sent to investigate the crash and finds that the ship is mostly intact, and appears to be have been sabotaged from the inside. among the wreckage are bodies of Eclipse mercs, Asari indentured servants, and a young human Biotic. the Asari all have their hands bound and point-blank gunshot wounds to the head, while most of the mercs have wounds consistent with a large singular biotic explosion, which parts of the vital systems of the ship also show damage of.
a Salarian Spectre (possibly Jondum Bau) soon appears on the scene and says that he's investigating the origin of the transport ship and wants the local authorities to coordinate with him on their investigation. they find that the onboard records of the ship were manually expunged prior to the crash, and they also learn that the young human Biotic is a student that was recently reported missing from a prestigious Biotics university on Earth. the Spectre takes the wreckage back to the Citadel for in-depth analysis of its systems, while tasking the local security official (and the group of people he has recruited or deputized for the matter, or so i had planned in the tabletop game version) to follow-up on the lead of the Biotics university. they find things to seem mostly normal there, but learn through some sleuthing and cryptic suggestions from nervous students that sometimes some of the students get "recruited" into a special program, and then just disappear.
in the tabletop RPG, i had planned on the party having the choice to also investigate any reports of Eclipse mercs kidnapping Asari indentured servants, and that would have led back to Ilium, but it might work better here if that's what the Spectre's investigation yields when he is able to recover fragments of data from its records. either way, after tracing the lead to Ilium, he learns of a mysterious "Syndicate" whose recent activities seem to be kidnapping powerful Biotics from all over the galaxy for unknown purposes, and he also gets a tip from a Turian informant on Ilium that points to the transport ship's origin being Omega. so the Spectre decides to further investigate this Syndicate while he tasks you with following up on the lead to Omega.
the party gets there, but it turns out to be a setup and they are briefly captured by Eclipse mercs, but are freed by a Turian who only says his name is "Archangel", and that he's been investigating Eclipse's recent dealings in shipping tainted eezo. the party here would have been given a choice to either help Archangel assault an Eclipse base or pursue the bogus Turian informant, but either way they would do the other one second, though it would play out a bit different. meanwhile, the Spectre is able to send out a secured message that he has been kidnapped by agents of the Syndicate and is in a holding facility, but that he can have his ship relay them all the info he's dug up on the Syndicate so far. assaulting the Eclipse base yields records that they were hired through intermediaries of this Syndicate, and tracking down the Turian informant leads back to a supposed Eezo Synthesis facility that turns out just to be a non-operational front.
by following up all those leads, everything points to the financial headquarters of the Syndicate being run out of Bekenstein. so the party goes there and learns from a stymied reporter (possibly Diana Allers) that the Syndicate's dealings are very shady, with one of their subsidiaries having something to do with this whole Synthetic Eezo breakthrough but with things just not adding up, such as some deep analysis tests of the Synthetic Eezo seeming to indicate that it contains biomarkers. with her help and the records from the Spectre's ship, the party learns of an off-the-books labship that the Syndicate maintains in a remote location in the dark space near the Boltzmann system.
they go there and they discover that the supposed "Synthetic Eezo" is really just the biological Eezo of tens of thousands of kidnapped Biotic people who are rendered catatonic and hooked up to machines that continuously extract material from the Eezo nodules in their nervous systems. even worse, they are purposely put into a state of constantly experiencing pain or fear or something in order to stimulate their adrenaline response, because that improves the Eezo yield from the process. the party confronts the director and lead scientist of the labship, who it turns out had lost multiple relatives who worked on an Eezo mining facility and were killed in an accident. he maintains that mining Eezo is a dangerous business and that millions are lost in accidents or occupational hazards every year, and that he is justified in trying to develop an overall safer alternative to that, with the sacrifice of a few hundred thousand being worth it in order to save millions, in true Utilitarian villain fashion. he said it started out as a volunteer process of getting people to just donate Eezo, but that didn't prove to yield enough for his goals, so he escalated it from there and lost his moral compunctions somewhere along the way.
the party would have been able to decide to either kill him and free everyone from the labship, agree with him and let him do his thing and become the new benefactors, agree with him but force him to stop the artificial pain/fear responses and make it a more humane process, or turn him over to the proper authorities. in most cases they also would have the option of turning over the research into voluntary donations of biological Eezo to proper medical authorities, to hopefully develop that into something useful. tbh i dunno which choice i would want to go with for the canon ending in a set narrative. but there ya have it.
tl;dr - a shadowy Syndicate has their medical research tech branch announce a breakthrough in developing "Synthetic Eezo", but it's really just a cover story for how they are kidnapping Biotics from all over the galaxy to forcibly harvest their biological Eezo against their will. the director of the Syndicate lost some relatives in an Eezo mining facility accident and wanted to developed a safer alternative to that, but lost his moral compunctions somewhere along the way and became a monster.