Lupi was Molly O'Brien's Bajoran doll.
In 2372, when Molly told her father she was going to have a little brother, Miles asked if she was referring to Lupi. She corrected him, indicating Keiko O'Brien's womb area. (DS9: "Accession")
In 2373, Molly was holding Lupi while Keiko, who was under the control of a Pah-wraith, brushed her hair. (DS9: "The Assignment")
Lupi used to sleep right next to Molly on her pillow every night. When eight-year-old Molly fell through an energy vortex on Golana in 2374 and returned as an eighteen-year-old, it was the sight of her doll Lupi that brought back memories of her former life aboard Deep Space 9. (DS9: "Time's Orphan")