The Witch: Her Sword, Her Princess by evening_redness

Suletta is a swordswoman with an unknown past, who slays a dragon that no other knight could kill. According to the traditions of Asticassia, this means she has to marry the princess.

Miorine is a princess who is greatly dissatisfied with her status as a prize to be auctioned off by her father, the King. But Suletta is not exactly the type of spouse she was expecting.

As the two of them begin to get used to the idea of marrying each other, a plot to throw Asticassia into a civil war begins to unfurl.

(Rating is E for a single scene near the very end. The SabiNika tag isn’t relevant until literally the epilogue.)