Kai Syaoran felt guilt as he remembered what he had done this family and how he had failed them .He remembered the moment he decided to go down this path and even though he still believed in what he did ,this was not enough to assuage his guilt .With his powerful Dao heart ,it was imaginable how great his sin had to have been for him to be affected so .As the Failed Prince ,the one that suffered the most from his action was his little brother .
All his family had suffered but his little brother truly suffered .The debt he owed this brother of his was as heavy a Mount Tai .He was sure that even after creation came to an end and all things were but memory in his mind ,this guilt would still not fade and his pain would still seat within his heart .Even the thought of finding ways to repent before his brother had never crossed his mind since nothing he did would ever make up for his sins.
