(Black Fate spoiler) Arcahv will receive a Beyond chart, rated at 11.Considering how absurdly specific the unlock method is, how climactic the song is to the story, and that the song seems to be Hikari's counterpart to Taritsu's Tempestissimo (with similar covers and soflan trickery), all signs point towards Arcahv being a boss song. And yet, its Future difficulty is a 9+, very low for a boss. Seems like a great time to use that brand new 4th difficulty, no?...Or maybe it's already there, and no one's found it yet.
The Memory Archive pack represents the memories Saya has visited.Saya's soundtrack, Memories of Realms, uses almost exclusively songs from the Memory Archives; given that these songs have much more variety than the main story songs, and that Saya is stated to look into Arcaea (with Saya's Story chapter and song pack concerning a single memory in particular), it could mean that every song within the Archives is symbolic of a scene Saya has observed. Hell, the urban metropolis mentioned at the very end of her story sounds like it could actually be Modelista's memory specifically (the descriptions of "artificial glow", "nigh-infinite towers of man", and "dark vehicles roaring through the air" match its artwork very well).