From Granblue Fantasy Wiki
Flawless Prisms are primarily used to uncap characters. They are needed for intermediate stars on SR characters and early stars on SSR characters.
|Uncap story SR to 2★||1|
|Uncap story SR to 3★||2|
|Uncap SR to 2★||1|
|Uncap SR to 3★||1|
|Uncap SSR to 1★||1|
|Uncap SSR to 2★||3|
|Buy 1 Rainbow Prism from the Treasure shop||15|
|Buy 5 Flawed Prisms from the Treasure shop||1|
Flawless Prisms are found in the Violet Trial daily quest.