The following tale is set in Fire Emblem Awakening’s world, before the game takes place. I added personal headcanons to make this story.
Valldar named his child “Grima”, as she would be called this way her entire life as the Fell Dragon’s vessel. She can’t recall her mother, as she died when she was nothing but a newborn.
Later in her life, her only social contacts will be her father, Aversa and some of the Grimleals taking care of her. One of them is Mustafa, blindly following Valldar’s order because he saved one of his family members (or rather, he did not kill them...). He was like her second father at times, taking better care of her than Valldar ever did. At that time, she would occasionally see Henry visiting Mustafa too. He was a weird man, but his stories were interesting.
Valldar wished to take the Falchion out of the Exalt’s hands. When he killed the King of Ylisse, “Grima” was only 2 years old and he couldn’t leave the baby alone for much longer. He was expecting Victor to wield the Falchion to this war, but was disappointed he wasn’t. The rage he felt made his flux stronger and annihilated the Ylissean. Valldar waited 5 more years, until “Grima” was 7 years old, enough to be able to walk, talk and defend herself. Together, they went on a trip to Ylisstol, the capital of Ylisse. After all, a good tactician must know the environment where their fights take place… In the streets, she passes apace with Chrom (8yo), Emmeryn (14yo), Lissa (4yo) & Frederick, going incognito under capes. They only exchanged a look, but that’s officially their first meeting. Valldar saw that the castle was overprotected so he went back to Plegia with only a map, situating the main strength of the Ylissean army. It was also the first experience of “social life” for “Grima”, leaving her place of birth.
When she got back home, Valldar was busy studying the information he had gathered during their trip. He gave “Grima” a lot of spare time. Bored in her bedroom, unused to having so much free time, she discovers a very small hideout in her bedroom, full of diaries. Teached to be a killing machine since her birth, she has been called “Grima” by her father and therefore only knows that name. She only discovers the name her mother gave her when she found her mother’s diaries: Loustica. She started to read them all, not telling her dad about it. Thanks to Aversa being angry at Lou for taking her “place” as Valldar’s daughter, he will soon find and burn them, saying he doesn’t want to keep any memories of her, because it “makes him sad”. He told her Daraen was taken away and killed by the Exalt army when she was little, trying to develop a strong hatred feeling in “Grima”’s head toward the Ylissean’s royalty. She managed to keep only one of them, which she will always carry with her so he cannot find it. But she had a good memory, and all the information about the “outer world” was already floating in her mind & dreams.
Loustica learned how to wield a sword and use magic and had to be better everyday. She was doing her best to make her father proud, but it was never enough. Lou was often exhausted but never gave up. The mutual rivalry with Aversa pushed them farther and farther, as “Grima” was catching up on Aversa even if she was much younger. Loustica knew nothing about the world besides her mother’s stories. Aversa on the other hand used to follow Valldar away when he was leading the Grimleal and talking about their next steps to bring Grima back to this world.. Living in such conditions, she was brainwashed to sacrifice her well being to intense training sessions. Valldar spends the next ten years preparing “Grima”’s body and spirit to welcome Grima as a vessel. She had to train from dawn to the middle of the night, having a terrible sleeping schedule. Her body was pale and covered in bruises due to the intense training and lack of medical support. She became stronger going through all those calamities on her own. She even learnt how to use magic to heal herself and used some herbs to make tea to strengthen her body and increase her energy. In the beginning of spring when she was 17, Valldar sent her on a mission, thinking she was finally ready.