Shōgi is an exotic inscrutable game suffused with the impenetrable mystery of the orient! It's also basically the same scenario as western chess – a few high-and-mighty bigshots sending a lot of expendable nobodies to their deaths.
You are a just and wise ruler, and the Mandate of Heaven is yours. At least until someone even more treacherous and wily than you comes along and makes off with it.
The current regime is corrupt and weak, and must be overthrown! In its place you will establish a corrupt but hopefully significantly less weak regime.
The spears that make up the Emperor's glittering wall of spear-points have to be carried by someone, and stuck into somone else. That's you, in both cases.