Under these circumstances, Manus stepped forward, having single-handedly sent the core prospective Death Eaters, along with some of their supporters, to the Hospital Wing.
Not only that, he proposed establishing an organization that judged people by ability and centered on self-improvement, study and research, and sharing results...
There would be no fighting or killing, no need to take sides, and a clear relationship between effort and reward. Ability was the only requirement, and most importantly-joining would offer a measure of protection.
At the very least, out of respect for Manus, those who had already been sent to the Hospital Wing would not dare push too hard. Mere everyday exclusion was nothing compared with their previous circumstances.
Capable Slytherins who did not want to tie themselves to the Death Eaters flocked to it.
Incidentally, Lily and Severus used this opportunity to establish an open connection with Manus quite naturally, though their acquaintance had already been an open secret among those who knew them...
Now that Manus had a team, he began handing out some of his more peripheral research projects, mainly those with such low returns on the time invested that they never made it onto his schedule.
After all, as his various lines of research progressed, Manus would only accumulate more projects, and this situation would continue for quite some time into the foreseeable future.
Nor did Manus make them work for free. Besides providing guidance relevant to the projects and the necessary protection, he established a credit system calibrated to each project's difficulty and cost.
Credits could be exchanged with Manus for rewards. Since the system was still in its infancy, there were not many things available yet: for now, only some magical plants he had cultivated himself, various materials, and a few minor spells he had created.
These