Source and explanation:https://old.reddit.com/r/HonzukiNoGekokujou/comments/1epe57c/p5v12_clustering_all_chapters_in_the_main_story/

TL;DR: All chapters are clustered using the lemmatized word frequencies (color). Then, they are then plotted in a way such that chapters with similar word frequency signatures are put closer to each other, and vice versa.

Basically, the plot shows the relationship of the chapters: how close they are to one another. For example, the bottom right mostly involves commoners, no books, no magic. The top left is very different, all chapters there involve nobles, magic, and Myne now has access to books or the library to some extent. The bottom left mostly includes the end of Part 5, the war, the gods, and the Book. It is very different from the commoner time, but also not quite as peaceful as the time in the Royal Academy of top left. The chapters from the same volume aren’t necessarily clustered together, either. For example, the Epilogue of P5V12 is a lot more similar to Parts 1 and 2. In fact, the cluster with P5V12 Epilogue mostly contains chapters about one’s future or promises.