Who is She? (Nanatsu no Taizai fan fiction: Diane x King)

"Long, long ago..... There was a place where a great giant girl lived all by herself. One day she rescued an unconscious boy who washed up near a river. Afterwards, the two of them became friends. The boy had a very kind soul and taught the girl sorts of things... Even going so far as to make clothes for her to wear. When the girl got sick, he looked after her day after day.... The girl was extremely happy. The only thing that she ever worried about was the fear that one day, this boy would no longer be in front of her. And at last, that day finally came. The boy promised the young girl that he would return no matter what... And then he left. In the end, the young girl ended up losing her memories before the boy could keep his promise. Before she knew it, 200 years had passed. Even though he left, fate always brings them together, they formed a team together with five more people. But in our last battle when that girl, who was on the verge of death, was saved by that boy... She remembered everything.... Every... Last detail... And now both of them met this mysterious Holy knight in the kingdom that brought luck and love in their way... But will that knight fulfill it's mission to bring back the beautiful past of the two?"