Amoretta's Flask is a flask that holds Amoretta's life. If it breaks, Amoretta will die. It was almost broken by Opalnaria Rain after she went on a rampage in Dr Chartreuse's Alchemy room, becuase Lujei Piche would not help her create a Rune to help summon Grimlet. But, the only reason why Lujei did not help Opalnaria is because Lillet said not to, since Grimlet wouldn't assist in defeating Calvaros.
In one of the time loops, Amoretta sacrificed herself by letting her familiar Grimalkin break her flask, and the flames had incinerated Grimlet as well as herself.