How do you get Zirael layered db?

[Renfield]

Title

[lexilogo]

Pretty sure Zirael works like the other HR crossover weapons, you need Unity Symbols which are from the Event Quest "A Shocking Climax".

Zirael is also specifically an Ancient Leshen weapon (unlike geralt's witcher blades weapons which are a regular Leshen weapon) so if you haven't killed Ancient Leshen you might well be missing materials.