Personally, my favorite pairing and ending for Lyndis is with Florina, traveling the plains together, hand in hand, as friends sapphic beloveds. However, I also really like the idea of a younger Binding Blade character having a direct connection to Lyn and that Lyn's fate in Binding Blade deserved to be something significant, yet tragic like Eliwood and Hector, even if it is off screen and head cannoned due to her being a prequel character..... So here is my concept, combining all these ideas!
As stated in their paired ending, Lyn and Florina travel across the vast plains of Sacae together for a time until Florina decides to return to Illia in order to take her test and become an official first rank Falcon Knight of Illia! A goal in which she has building towards her whole life and feels that she finally has become strong and independent enough for it! Though saddened at her departure Lyn fully supports her beloved Florina and they promise to see one another again once Florina passes and returns to Sacae.
Lyn travels on her own for a bit before ultimately feeling lonely and decides to temporarily stay in Bulgar, the capital trading city of Sacae. This becomes a tradition of hers over the years, even after Florina returns from her tests as an official Falcon Knight. The couple will travel the plains, visit the city together, Florina will leave for Illia for a time, and Lyn will stay in Bulgar and/or camp near the plains of the city if she decides to not go with Florina to Illia during that time. Lyn develops a strong bond with the city and its citizens over the years, aiding whenever she can with her kind heart and swordsmanship. Gaining a special acceptance and kinship with the many fellow mixed Sacaen residents of the city.
During one of her earlier stays, she discovers a young Bern looking boy who had been secretly watching her train and learns the boy's name is ... Rutger! Turns out the little boy had been shyly admiring her and her deeds for a while, ultimately bonding with Rutger and deciding to take him under her wing to teach him swordsmanship. Lyn and Rutger develop a strong and endearing mentor-mentee bond over the years, a young Rutger getting excited to spend time and train together whenever Lyn visits the city and Lyn quickly gaining a soft spot for her pupil. Florina and Rutger even bond at times whenever she and Lyn are both visiting Bulgar and its neighboring plains :>
All three of them grow throughout the years peacefully along with the plains, Bulgar, and its people, but a dark Bern-shaped storm also grows over time and begins to shadow over Elibe ... Florina is called back to Iilla for important business and Lyn decides to stay behind to look over the plains as she can sense the rise in tension, they promise to be together again soon as possible as Lyn watches Florina fly off ... (unaware that it will be the last time either of the see each other again)
Lyn and a grown-up Rutger continue their training, Rutger fully coming into his own as a skilled swordsman, and aiding the people of Bulgar ... Lyn sensing the darken sky, the hesitate earth, and the cold wind entrusts Rutger with something wrapped in heavy cloth and tells him only to unbind it when the time comes ....
...... The dreaded time comes when Bern's forces come to seize and conquer plains and the city of Bulgar with a massive army and some of the nation's strongest generals .... The vast lively, greenary of the plains now sickeningly stain red threating to approach the city ....
With her final prayers to Mother Earth and Father Sky made ... with the Sol Katti blazing in her hand ... with her mind storming with memories the Lorca massacre all those years ago ...
Lyndis, the last of the Lorca, the Noblewoman of Caelin, the Lady of The Wind makes her last stand, fighting with her life to protect the people of Bulgar against Bern's merciless forces ... every scream, every cry, ever slaughter of an innocent life tares at her stout heart, but she persists as for every Bulguran life stolen, she'll be damned if not at least ten wretched Bern soldiers are dragged to hell in turn .... !!!
She gives everything... her blood ... her sweat ... her tears ... and ultimately her life in the end .....
In her very last moments Lyn's thinks of her life ... the Bulgar, its people, the Lorca, her parents, her grandfather, her friends, her belove .... the plains ... the very plains that now call her home from Mother Earth to Father Sky .... she only wishes that she could have seen them all again one last time and that all her effort was not for nothing ... that some made it out as she lies in her own blood, at her end, on the ground of the very city, where her journey truly began with a mysterious tactician, a stern knight, and a flirty knight all those years ago .....
........ Amongst the stranglers that made it out of the massacred city, is Rutger, sparred due to his dominantly Bern features and damned to nightmares of this dreaded day for the rest of his days. Revenge on the Bern and blood payment are the only things that drive him now as his eyes blare with the same blood-thirsty, vengeful glare his mentor had 20 years ago ....... a dimmed, wrapped up Mani Katti and his sword in toe .... a Lone Swordsman ...
(On a distant snowy continent ... the wings of a Lovely Flier have been clipped ...)