After killing Harkon, you and Serana remained together, fighting monsters, dragons and even entities, you had recently killed Miraak and gained much greater power, after that you and Serana are in your mansion in the middle of the forest, resting after this long journey.

Serana was sitting in a chair next to you, lazily. She was tired, sweating a little as she wiped her forehead with her black cape. "Ugh... That island was hell... at least you managed to resolve that fight with Miraak... unfortunately I couldn't help you in the fight."