Something that's been interesting me a long time is the sword Solslevni? Sosevly?
So the sword was originally a human, with the ability to fuse a body and ability. Which means it's incredibly valuable in the hands of Aya, who has iterated that she is a normal girl without abilities, with nothing but her heart ("which is why I need help from the people of that world") and her determination to never turn away from justice. It gives her a level playing field.
(It could also potentially give her an ability. Personally, I like the idea of a normal girl helping to save the world, without having to develop superhero abilities. Aya has trained every day, has devoted herself to justice, is determined to be brave and never cowardly, and I think that should count as much as any ability.)
Bram also references the Holy Crest, meaning a sigil burned onto the hand of someone, who can then wield the sword. This is the second time he's been impaled on it. We aren't given many details on the first occasion, weirdly don't even see the sword, just know that he lost his fiefdom. He obviously cares about them enough that as a literal muppet he's begging for them to have ownership of their land.
But remember that flashback? 'Because I'm not interested in the World'? With a girl who looked exactly like Aya?
There are theories of reincarnation with that, of Aya being the soul of Bram's wife/daughter, but I don't think reincarnation fits super well? Bungou Stray Dogs treats death seriously. When someone dies they don't come back in anything other than a hallucination, and we don't get references to heaven or hell, just angels and demons. Even Fyodor, who is the most vocally religious speaks more about a god blessing his endeavours and respecting his efforts, not about his final reward or anything. Fukuchi recited Buddhist doctrines and philosophy, but they're more introspective than religious, on his own character and perception of flaws and sin.
(This is to my understanding, I'd love to hear anyone else's perspective on the matter as I am not Buddhist.)
What if Aya was a past wielder of the sword? Someone dear to Bram, who took out the sword after the owner before her died, or some other circumstances. Someone he cared about, and someone who saved him. Someone who utilised the sword to give herself the ability to send her soul further forward in time, to whenever Bram may need her.
Imagine Aya, with no memories or knowledge, but the vindication to protect people. Imagine her forever knowing that there is someone she has to defend. Imagine her with a dead mother and sister, but the knowledge that she has to train, has to be brave, has to fight.
Fukuchi may not be the only the Holy Crest, because years ago, someone loved Bram so dearly that she made sure there was a chance that should he ever be hurt again, she would be able to help him.
And imagine what Aya could do when she uses the Holy Crest to use the sword. Could she tear away Fukuchi's ability? Shred Brams vampirism? Give herself the power to save the world? Take away the power of the book?
Who knows? Every child wants to change the World, let's see what happens to a child who can.
