Mass Effect 2 & Mass Effect 3
The drell homeworld of Rakhana once teemed with life, its arid plains home to spectacular insect and reptile analogues. But the drell took to industrialization early and did not realise the extent of the environmental damage they caused until it was too late. With their topsoil depleted and oceans too acidic to sustain life, the drell were situated for a massive population crash by 2025 CE.
It was then the hanar stepped in, mounting a large-scale rescue operation to bring drell to the hanar homeworld, Kahje. As wars erupted over what resources remained on Rakhana and billions began to die, approximately 375,000 drell escaped in the exodus. To repay their debt, the drell entered into an agreement with the hanar. Called the Compact, it states that the drell would assist the hanar with tasks the hanar cannot physically perform. Today, high-ranking hanar are often inseparable from their drell attendants.