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Dark Matter Arcane Glyptics Campaign - PLUS
Geas Fete notorious monsters in Reisenjima through Arcane Glyptics can be engraved with arcane glyptics up to twelve times at no additional charge, with the equipment receiving the same benefits as if they were engraved with dark matter.
Based on this wording this means that the Geas Fete notorious monsters can be augmented with dark matter.
When I read the Japanese text:
バトルコンテンツ「ギアスフェット」の戦利品のうち、醴泉島で入手した装備品に対して無料でアーケイン・グリプトを付与できます。回数は12回で、アイテム「ダークマター」を使用した場合と同じ能力が付与されます。
I would translate it along the lines of:
The spoils(drops) from Geas Fete notorious monsters(reisenjima) can be engraved with arcane glyptics up to twelve times at no additional charge, with the equipment receiving the same benefits as if they were engraved with dark matter.