Leeches were used medically for millennia on ancient Earth but were largely superseded by technology. Hundreds of years later, a chance discovery on Kachirigin revealed some very valuable properties of the native creatures. Kachirigin leeches can painlessly filter impurities from the user's blood, so can be used as a cure-all for hangovers and the worst affects of certain addictions. They are prized by the wealthy and hedonistic, and have an almost cult-like following.
— In-Game Description
Rare goods increase in value the further you travel from their point of purchase.