In brief, the little sprite-like girl on the Kuro no Kiseki key visual is a form of communication device. Furthermore, I believe the figure is contained inside the old orbment Agnes is concerned with, much like a ‘genie in a bottle’

Looking closely at the art, a number of cues give this impression. The most forefront is that the girl and the orbment both give off the same blue glow. This doesn’t mean anything by itself but could suggest there is a link.

As for communication, there are a few hints here. The girl has some kind of antenna or satellite device on her head and ears, possibly for helping to pick up signals. Around her there is a magic circle with irregular, frequency like bars, much like you would see on one of those Windows media Player apps from the past. Lastly, note the ribbon like sashes that flow from the small girl. They don’t seem to be following any sort of gravity, and of all the positions to be in, they are pointing directly at the hand of the shadowy “Van”-like figure and the large creature’s mouth. Perhaps these ribbons act like audio jacks, and connect beings together?

I think the purpose of the old orbment is an ancient device used for communicating with creatures/individuals from the Beyond. We know the theme of the arc seems to be heading this way with all the ‘shackle imagery’ (and indeed the other key visual shows the same shackles attached to the orbment, suggesting a “link”).

This creature then, with its more-than passing resemblance to McBurn’s true form, is from the beyond, and some figures form the ancient past devised a device that could connect the two and overcome the communication barrier. I think the creature cannot speak in the conventional manner, or at least it doesn’t appear to have a mouth, necessitating an intermediary to speak. McBurn, as a merged figure, doesn’t have this limitation.

Agnes and her family for whatever reason may not be able to use the device, but this Van figure might have some special condition that allows him to use it, much like Rean was a candidate for Valimar. In fact, I am expecting the link between the two two to work in a similar fashion.

Generally, I am expecting the Sept-Terrion of the arc to be Wind, which is connected to the idea of rationality, the mind, intelligence and communication. Having a device like this at the centre would be a perfect fit for that theme. Perhaps the ancient wind tribe created these communication devices long ago.

All in all, I believe Van will obtain this device and unlock its communicative abilities, forming a bond with this creature at some point in the story.

Further questions:

• Is there a link between this old orbment and a Sept-Terrion? Every known way of crossing the ‘shackles of Aidios’ has been by using or ingesting a piece of one: the Gnosis was made from Pleroma, the ‘eyes’ of Mirage, whereas the Ishmelga-Rean timeline broke the barrier using the combined powers of Divine Knights (Fire and Earth). Some aspect of the remaining Sept-Terrion, (probably wind) could be at play. One could even make the link between what Gnosis allows someone to do with Demonise, and what happened to Weissman.
• Is there more than one of these devices?
• Is there more than one of these creatures? And if so, does each have a device, and they are bound to it, or they universal translators.
• Why does Van have the potential to use this, assuming the shadowy figure is indeed him?