It could be a rogue vampire who has a vendetta against Bella or the Cullens. This vampire might be out for revenge and attacks Bella, which is how she ends up covered in blood.
One possibility is that it's a misinterpretation. She might be covered in something that looks like blood but is actually something else, like a special potion gone wrong in a magical fanfiction setting. This could lead to all sorts of misunderstandings and adventures as she tries to clear her name or figure out how to reverse the effect.
Armin could be the storyteller. Sometimes characters take on this role to provide a unique viewpoint or to drive the narrative in a particular direction. But we need to know more about the story to confirm it for sure.
Armin is still alive in the manga. The story developments don't result in his demise. His presence remains significant and continues to shape the narrative.
Another theme is his relationships. His friendship with Eren and Mikasa is frequently explored in different ways. Some fanfics might focus on how his relationship with them changes as they all grow older and face different challenges.
A Jean x Armin fanfic often explores their unique relationship. It might focus on their growth as characters in different scenarios. For example, in some fanfics, they could be on a mission together and develop a deeper understanding of each other's strengths and weaknesses. This type of fanfic can also delve into their emotional bond, perhaps showing how they support each other through difficult times in the fictional world they inhabit.
A Mikasa x Armin fanfic often explores their unique relationship. It could show their deep emotional bond that might have developed over their shared experiences in the story. For example, their mutual understanding of the harsh world they live in and how they support each other through difficult times.