Judeim is a yet to be seen entity with great power that's believed to be the "true form" of Alba and Soiree Meira (his power is split between the two, he originally speaks in a duo toned voice). He is hinted to being an alien warrior who had once worked with Jivatma as a comrade-in-arms in Addes, known then as "The Dark Fang" or "Fang of Darkness". A certain incident caused him to lose his memory, seemingly ending his purpose and existence. It's insinuated that Jivatma is trying to revive him through Soiree.
Luise also knows about him, but chooses to keep the knowledge to herself, wanting the brothers to live a normal life of happiness. She promises to tell Alba all that she knows in their endings.