The 'the beginning after thr end novel' likely tells a story of transformation. It may follow a protagonist who has experienced some sort of ending, like the end of a relationship, the end of a way of life, or the end of an era. And then the story focuses on how they navigate through this new beginning, facing new challenges, making new friends or enemies, and learning new things about themselves and the world around them.
I don't know the specific main characters since I haven't read this novel. Maybe there is a young hero or heroine who is leading the story through this new beginning.
The Beginning After the End manga has indeed finished. It provided a satisfying conclusion to the characters' arcs and the overall narrative. Maybe there'll be spin-offs or related projects in the future, but for now, the main story is complete.