One of the many things I appreciate about this series is how Kei isn't a gray straight man character either. His voice acting was quite lithium in the anime, but he's still a real person with his quirks and jokes. I could very easily see a lesser mangaka making him nothing but a sort of reflection surface to allow Makoto and Chinatsu to stand out more. Fortunately that didn't happen and he stands on his own, just like the others.