It's just a text to get a feel for the world of Tsubasa. To put it simply, it's the story of Madara's previous life (tragedy of the original work). When Madara was in the cave, he was accompanied by a life that he couldn't see. After many years, he woke up and faced the scene of Madara's death again, and then turned black, changed his destiny, and reversed the story of time and space!