Disclaimer: I don't own Fire Emblem and their characters except OC.
The stoic mercenary who is notorious legend as the Ashen Demon is investigating in the forest alone on what cause the mystery deaths and getting a mineral for the kingdom noble.
Byleth Eisner who is doing her mercenary job in the forest have a bad feeling about the forest. As there is no animals living in this forest. Byleth remember her father inform her before going to the forest. Was many mercenaries, nobles, commoners, knights, soldiers, mages and others went inside the forest and mysterious died in the forest from the kingdom noble's report on the forest and there was rumor that a rare mineral was very valuable and according to the kingdom noble.
That rumor said the rare mineral in olden days of Fodlan was said to craft beautiful accessory with magical property or forge power weapons that could slay powerful warriors. It is said a sword forge from that rare mineral have once beaten an army or a ring crafted from that rare mineral said to boon a weak mage potential in a boost wearing that rare mineral ring in the old days of Fodlan. It is said that selling that rare mineral could set you for life for 20 years and it is said that fable mineral came from this forest. And it an once in a lifetime to the kingdom noble and that the kingdom noble is not going to waste that lifetime away and the noble will pay her father's mercenary group greatly if they succeeded in getting that mineral for the kingdom noble.
Pragmatically the kingdom noble also want the mysterious death to be investigated and maybe stopped, just so the kingdom noble will get a good standing within the Holy KIngdom of Faerghus. The kingdom noble assumed it was a group of very talented bandits that caused the mysterious deaths in the forest. And so the noble hired the Jeralt's Mercenaries for the job in the forest.
Jeralt also assuming it was bandits that cause mysterious death have send his daughter Byleth to kill the bandits for their crime and get the rumor mineral if she found it in luck while wandering in the forest for the bandits. Jeralt have good faith in his daughter to get the job done.
While finishing remembering her father's report in the forest is Byleth who is having trouble finding the bandits hiding in the forest and thought.
'This silent is disturbing in the forest?'
'I'll better find and kill that group of bandits soon and reunited with my father soon.'
'Is the mineral a gem or a metal?'
'Wait a minute? Was it really a group of bandits that cause the mysterious death in the forest?'
'There is no animals living in this forest?! And is this really the works of bandits?'
'This forest lurk of danger. And I don't think it was bandit's work that cause these deaths in the forest.'
As she walk further in the forest, Byleth notice some corpses and weapons on the ground. Some of these corpses are mercenary who got killed in the forest or mages wearing weird clothing that is unknown to Fodlan. There dead bodies have given a foul odor that disgust Byleth despite unable to express her emotion.
And out of nowhere the dead bodies of mercenaries and mages have rise up from the dead! Giving a silent shock to Byleth as they risen from the dead and tried to kill her, however the undead actions are futile as the Ashen Demon kill the undead with ease as they got killed easily by her iron sword and were nothing in face of the Ashen Demon. As Byleth finished killing the undeads, she find it weird for the three zombified mages wielding books didn't vanished into nothing like the other zombies' weapons she killed?
The mysterious three books that weren't vanished in a quick easy battle were pickup by the Ashen Demon and store it in her inventory for now, unaware the three books she pickup are really the fable Heroes' Relics created by forbidden insanity unknown to the people of Fodlan.
'That fight was disappointing and these three books are weird?'
'I wonder why these books didn't vanished after killing those three disappointments?'
'These corpses have risen up and tried to killed me in surprise. I better keep my guard up.'
The Ashen Demon continue her investigation in the forest and killing every undeads in her way as she went deeper in the forest and she discover a large gem with six eyes marking on the gem-like mineral. Was this rare mineral that the kingdom noble talking about?
'The rumor mineral was real?! And it huge?!'
'Guess that kingdom noble was right. Is the noble willing to accept the mineral with it creepy six eyes?'
'First the undeads? Now the rumor huge mineral is real? What next some type of monster appearing out of the gem?'
As Byleth look at the weird gigantic gem mineral before her. The Ashen Demon sense something within the six eyes gemstone and the gem mineral manifest a shadowy apparition in a form of a serpent with six wings glaring with it six red eyes. The apparition give a dragon roar to the widen eyes Ashen Demon while she hold her sword ready to fight the apparition.
'Is this creepy gem a mind reader?'
Byleth fought the shadowy dragon. While she aim to slash the gemstone in hoping that breaking the gem will kill the apparition. Byleth have dodge the Dark Spike the serpent have made to kill mercenary. The fell dragon summon his risens to attack Byleth which she counter in ease. Grima summon thunders to strike the Ashen Demon dead but Byleth swiftly escaped the thunder strikes. As Byleth got close to the gem and almost break the gemstone, the Ashen Demon was counterattack and weakened by Grima's dark magic.
As hope was lost for Byleth as the shadow apparition was about to kill the Ashen Demon with his dark magic. A magical manifestation appearing in front of Byleth and protect her from the fell dragon attack.
It was the girl that appear in Byleth's dream that protected Byleth from Grima's darkness and the dream girl use her magic and weird symbol manifested as she perform her magic on the fell dragon to seal Grima back in the gemstone and heal and restore Byleth and her clothes with her magic.
The fell dragon last word before being sealed and shattered by the dream girl magic are. "You only have delayed the inevitable little girl...I'll be back." Grima was sealed by the little girl's magic and the dark gem have shattered.
Appearing out of the shattered gemstone was a hooded boy with six eye marking on his clothes. Who landed on the ground after being free from gem imprisonment and was weaken by the dream girl magic.
Byleth felt something weird in her heart when she saw hooded boy who was freed from the gem. Her own heart have started to beat and felt an unknown emotion starting to manifest when she saw the boy in his six eyes clothing. Byleth decided to take the boy with her when he wake up from his sleep.
The mercenary have decided to wait for the boy to wake up from his slumber. And when he started to wake up, he sluggishly stare at her and said.
"...Lu..Lucina...?"
Byleth shook her head and said to the boy in a near monotone with a slightly jealous tone. "I do not know who is this Lucina is, but I am not her. I am Byleth, a mercenary. Are you alright?"
"I," The hooded boy tried to speak, but he was coughing from his weaken state. So Byleth have given the boy some water to drink which he drank greedily without any thought. "Thank you, I am called Robin. I am just a bit lost here and I am uncertain, but any chance if you know of Ylisse?"
Byleth shook her head negatively again much to hooded boy named Robin's dismay.
"I know not of this Ylisse and I am fairly new to these parts myself. What I do know is that we are near to the Holy Kingdom of Faerghus in the continent called Fodlan."
Byleth have pick up Robin and carried him to come with her to her father's mercenary group to recover.
"Wha-? Hey?"
"Not only you are lost, but you are also weakened by something."
"Much of you is currently unknown and I feel it would do me no good to leave you alone here. Taking you to Holy Kingdom of Faerghus where I, my father and my company is temporary residing in could benefit both of us."
Robin's simply questioning in his weaken state.
"Why?"
Byleth shrugged to Robin's inquiry with a response.
"I do not know why. But I feel something with you that I'm not sure I can understand."
After hearing Byleth's response about her action on Robin. Robin passed out and Byleth carried him to be with her as she travel back to the Holy Kingdom of Faerghus in hoping to understand the weird feeling about Robin within her heart.