The story's narrator is Odin
The two ravens flying over Oslo are rather unquestionably Huginn and Muninn, and the notes how the narrative is switching between eras sounds like Odin is switching his clairvoyance target. We already know that he foresaw both Goetia and Foreign God, so he definitely has the ability to observe the modern day and thus making him be Narrator All Along very likely.The being standing next to Percival isn't actually his partner
As seen in one of the preview illustrations, SOMETHING is seen next to Percival. However, look at Perci's face. He's wary of this entity. implying that it's another one of Caster's familiars.- Jossed. It's his partner, Rider Sinfjotli.
Bragi was Odin (in disguise)
He is stated to have two crows with him, all his artwork has him with an eye shut, he is a skald which was a profession connected to illusions and prophecies, he was the person to first talk to Aslaug about Ragnar, and "Bragi" is the name of Odin's son. It is a well known fact about Odin that he goes around in disguise, and Fate/Grand Order has already used that, so why not here?Saber's partner is an Extra Class servant
The novel clearly states that eight servants can be summoned in this holy grail war. All of them are given artwork, except for Saber's partner. By this we can assume that their nature and/or identity is a big twist, which would make sense if it was an extra class servant. Not to mention, since this novel is a sequel to Fate/Apocrypha, it has already been established that Extra Class servants can be summoned by the Holy Grail.The Caster is Baba Yaga
Caster is stated to be a woman capable of switching between an old witch form, a seductive young woman or a child, and she can summon forest creatures which implies an affinity for them.Assassin's moniker
It's blatantly obvious that the woman who's teamed with Caster is a Hassan, but what we don't know is her method of killing. Perhaps her moniker is "Hassan of the Breathless Rope" considering her long, braided hair evokes the appearance of a noose?