The blessing of immortality was bestowed upon them to avoid misusing it, the God of Destruction told them that the only way to activate this blessing is through a ritual where a royal bloodline will need to feed blood to the spell circle to keep it activated. Of course, the one in the spell circle was blessed with the same blessing of immortality and wouldn't die. However, the process of losing blood cannot be ignored. It was even unknown if these blood can be restored by the blessing given to them.
