I am stupid and I didn't notice that the bat necklace Emalf wears actually belongs to Adauchi. He wears in whatever that one piece of art on the left means and in the School AU (if you also look at the chibis in the chara sheet you can see Adauchi is wearing it and Emalf isn't, meaning there is only that one necklace). The bat is Ivlis' symbol as you can see the exact shape marking his door (it kinda resembles the silhouette of his scarf wings too). So in the main timeline, Adauchi left behind the necklace to cut all ties with Ivlis and then Emalf started wearing it.
There's also the thing that one would likely get upset if a guy openly wore the necklace of their missing child they may not see again, so the fact that Ivlis just lets Emalf do it probably means he loves him very much as another family member.
Ah, but I could be wrong, i am just overanalyzing pixels and nothing has meaning. Many such cases.
