Shane had heard of 'gradeless and qualityless' skills and also about domains that had unique traits. Both were unique and extremely rare characteristics that one could only obtain by solving [Universal (Mythic)] missions.
At least that was what his aunt Kia had told him once. However, she didn't even know what these missions were because they were not listed in the common mission segment.
Other than completing missions, one might be able to receive such a weird gradeless and qualityless domain skill directly through the system awakening like Shane had received [Artemis' Blessing] and his Innate Skill [Taming].
It must be the latter option because Shane doubted that someone like Ilya would have been able to solve a Universal mission.
He might as well be completely wrong and Ilya could be a powerhouse in the Advanced Dimensions and was hiding within the Basic-Dimensions after finding a way to trick the system.