He's the real Oda Nobunaga, though most people don't know it. The political pressure of the role got to be too much, so he found someone who looked identical—a guy named Saburou—and basically swapped places. While the fake Nobunaga handles the seat of power, he's been free to move around the country doing his own thing.
Eventually he ended up taking control of the Akechi Clan when their leader died without an heir. Now he operates as Akechi Mitsuhide, working under Saburou (the fake Nobunaga) in what's become a pretty convenient arrangement for everyone involved. It's a weird setup, but it works.
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