In the ages of kings and queens, the large kingdoms wedged into wars hungry for power trapping the small kingdoms into them. Somewhere, there was a small kingdom ruled over by a princess (Rin) (for some unknown reason) that had offended the other kingdoms. As a sign of peace, the princess was to be put to death by hanging.
The song starts with the princess and her childhood friend and most trusted knight (Len) in a pavilion in the middle of a rainy night. She told him about her dream of a kingdom that was peaceful and safe. For the last time, she instructed him to see her on her execution with a smile and he agreed with a bow.
Next he is showed in his room waiting for the time for execution he reminisced of his (presumably) fallen comrades and of the princess. It is hinted that it might be him that advised the princess to comply with the enemies demands and calls himself for being a coward for it. Finally realizing that the princess was just forcing the smile on her face at the pavilion he decided that he will rescue her no matter what and was going to say what he really wanted to say the previous night even if doing it would brand him a traitor and risked the life of the whole kingdom.
He fought his way in to the town hall where the execution was held losing his right arm and left eye in the process. He tells her that he didn't deserved to be her knight and he cannot fulfill her request. The princess, saying it was okay because she was happy to sacrifice her life for her kingdom and not to rescue her, smiled and pleaded one more time to smile for her while they hanged her.
Shouting no, he told her that he did not care for what happens to him and the kingdom as long as she was alive. Just as the lever was being pulled, the knight cut the noose off her neck, and ran away with the princess, saying his life was with hers till the end.
As a result the kingdom was destroyed by the other kingdoms with the whereabouts of the "unknown knight who obstructed the execution" and the "dirty princess who had runaway from the execution" unknown and they were likely be talked about in another story.