Factsheet
Betrayal as Strategy: Kobayakawa Hideaki and the Game Theory of Sekigahara
A new reading of Sekigahara, Japan 1600: the betrayal that decided the battle, reinterpreted as strategy. A historical novel reconstructs the Battle of Sekigahara from one young lord's decisions.
| Author | Sagara Sei (相良 静) |
| Kindle edition | Available for pre-order (releases October 2, 2026), US$5.99 |
| Paperback | Coming mid-October 2026, Expected price US$12.99 |
| Japanese edition | 裏切りの戦略 (Kindle, October 2, 2026) |
| Book page | https://sagara-sei.com/en/books/sekigahara/ |
| Press kit | https://sagara-sei.com/en/books/sekigahara/press/ |
| Contact | press@sagara-sei.com |
Summary
In 1600 the Battle of Sekigahara decided who would rule Japan, and the change of sides by Kobayakawa Hideaki, eighteen years old, decided the battle. This novel reads him not as an indecisive traitor but as a lord who, watching Tokugawa Ieyasu advance west, chose his own ground and his own moment. The story follows his actions in order; the Analysis explains his choices with game theory and tests them against other explanations; the Evidence section marks where the sources end and inference and fiction begin.
The book's hypothesis
No contemporary document ordering Hideaki onto Mount Matsuo survives from either side. Rather than ask who put him there, the book assumes he chose the place and the moment himself. On that assumption, keeping his allegiance hidden, taking the mountain and moving on Otani Yoshitsugu the moment the battle opened read as one line of decisions made to keep his house alive — the work of a strategic genius, not a hesitant youth.
Method
Keep every event the sources record; infer only the decisions they alone cannot settle.
- Events confirmed by the sources are not changed; the research interpretations adopted are named in the Evidence section
- What the sources cannot settle is treated as a decision model, with every assumption written out
- The "probing shots" (toi-deppo), Ieyasu's guns said to have forced Hideaki's hand, do not appear in contemporary sources; the book does not use them