Y’know, I always did wonder why Leonie wasn’t Byleth’s friend from the get-go. Seems silly that Jeralt left Byleth somewhere for that single mission.
(Note: I’m going with the “memory issues” Byleth for these headcanons, as they seem to have trouble remembering details of things that happened before Sothis woke up.)
When Jeralt and his mercs came to Sauin Village, Leonie was really excited to have such great heroes in her tiny village. But then she saw that one of the mercenaries was about her age.
During the downtime between dealing with the poachers, Jeralt would train with Byleth. Leonie would watch and quickly gathered the courage to ask Jeralt to train her, too.
Jeralt agreed to take her under his wing and taught her the basics of fighting.
Byleth was leagues ahead of Leonie in terms of skill, but that didn’t stop her from declaring them her rival.
At first, Leonie would get upset when she couldn’t land a blow on them, but one day she asked Byleth what they did once training was over and they had some down time.
Byleth shrugged and said that they would do weapon maintenance or inventory their supplies or any of the upkeep tasks that had to be done.
Leonie was shocked to hear that her sworn rival’s entire life seemed devoted to fighting, without much in the way of hobbies and the like.
When Byleth said that Jeralt would sometimes take them fishing, Leonie basically scooped them up and took them on a fishing trip. Just for fun.
Leonie spent most of the time chatting about her life and silly, kid things. Byleth said very little, only answering direct questions, but they paid very close attention and seemed to relax a bit as the day went on.
Despite never smiling, Byleth told Leonie that they really enjoyed spending the day with her.
They kept going on little trips like that in and around Sauin until the poachers were all dealt with and the mercenaries went on their way.
On their last day in the village, Leonie gave Byleth her fishing rod, saying that she’d like to go fishing again one day.
Byleth apologized for not having anything to give her in return, but Leonie said it was alright, just asking that they remember to visit.
Byleth said they’d try. They never did, however, and the next time they saw each other was at Garreg Mach.
Leonie isn’t all that surprised to see Byleth at the Officer’s Academy. After all, they’re the famous Blade Breaker’s child; of course they’d wind up at Garreg Mach.
What did shock her, however, was how Byleth didn’t seem to recognize her at all.
She was frustrated that there wasn’t even a hint of familiarity in their eyes when she spoke with them, and eventually, she confronted them about their sudden coldness.
Byleth hesitated a moment before explaining that they couldn’t remember much of their time in Sauin. They remembered poachers and fish but none of the details.
They apologized for forgetting, and Leonie, while still upset, forgives them on the condition that they go fishing again.
Byleth says that they’d love that.
Afterwards, when they’re cooking their catch, Byleth tells Leonie that they’re starting to remember just a little bit of their shared history. Mostly about how much they enjoyed eating the fish she grilled.
Leonie’s glad that they remember even a little bit, and they spend a lot more time together, just fishing and talking.
This time, Byleth smiles.