These are the splash pages, or chapter pages if you prefer to call them that, that usually kick off a chapter and just feature a logo and illustration. Black and white ones only here, the full color ones are under the Color section.
Fun bit of trivia: this splash
and this splash
were used for the same chapter, but under different circumstances. The first one was the splash used in the Zero-Sum magazine version, and the second one was in the tankoubon version. Why did Kouga change it? Who knows. The original was quite nice.