(from ebookjapan):

The real son of Kuroda Kanpei, a military strategist who had served Oda Nobunaga and Toyotomi Hideyoshi, was killed by Nobunaga and Hideyoshi while Kanpei was imprisoned by Araki Murakeshige.

Although he served them both as a military strategist, Kanpei, bent on avenging his own son's death, plotted to have the two men killed together.

Nobunaga was killed by Mitsuhide, but Hideyoshi turned his misfortune into a blessing and became a natural successor!