Lamia are mortals who have been changed through love for an Overlord or its prakhutu. True love is hard to come by, and most servants of the Lords of Dust cannot truly claim to love their masters, but there are a rare few who do, and there are consequences for loving a fiend. These mortals find themselves changed, imbued with the essence of their love, and granted qausi-immortality. They will never age or sicken, but they can still be killed.
Most Lamia have the upper body of their mortal form, but their lower body has been replaced with something that represents their fiendish love. For most, this gives them the body of a tiger, taking after the Rakshasa, but those who fall in love with Masvirik, the Cold Sun gain the lower bodies of serpents. This transformation brings benefits, they gain some of the magical powers of the Rakshasa, and a tiger's body is better suited to violence than most mortal's, but it also brings sacrifices. Lamia, despite their intense love, cannot bear children or reproduce.
Lamia are shaped by their overlord, and seek to embody its virtues. A lamia forged from love for Tol Kharash will seek to dominate others, whereas a lamia enamoured with Sul Khatesh will hoard magical knowledge, perhaps even sharing it with others.