[Ariel_Saeba]

Ah, I think I've read about Satanael's line in the WN as well but not as clear as in the LN version (I think), so it's more to the latter with a twist (an old task force turning rogue).

Either Azazel or Baraqiel warned them, considering that the latter would train Tobio's group.

Here are the lines from the WN:

Spoiler for WN Quote:

Lavinia continued.

“I——Grau Zauberer along with the Gigori have been pursuing magicians who had infiltrated from the magical domain known as ‘Oz’——they were collaborating with a traitor within the Grigori, leader class fallen angel ‘Satanael’.”

Oz——,

Moreover a traitor within the Grigori——‘Satanael’.

While also being concerned about the movements of the remaining fellow students who were among the ‘Four Fiends’, also approaching Tobio and company was an otherworldly visitor they had not been expecting.


Thus begins, in the midst of the three way conflict between the ‘Grigori[55]’ who pursue Sacred Gears, the ‘Five Principal Clans’ who govern the Four Divine Beasts and the Ouryuu[56], and the ‘Wizards of Oz’ who had won over leader-class fallen angel Satanael, becoming the blade of the gang of the black wings, the story of the ‘Dog’ that slays an endless variety of supernatural powers.

This was the person, the one who would later become known as ‘Slashdog’——