This was a much weirder experience than I was expecting. Felt like I was Spongebob Squarepants wandering the dreams of a salaryman.
Notes I took as I read:
* If it's a curse to live in interesting times, it's also a curse to live in a manga. 80% of Kosaku Shima features people living basically satisfactory modern lives — working hard, yes, and not always happy, but stable and secure. The other 20% goes to wild places, and people get hurt in wild places. Killed, even. When you come into contact with Kosaku Shima, something interesting will probably happen to you, and you probably won't like it.
* There is a scene where a character hides in a closet to escape attention (in a small Japanese apartment). Later, there is another scene where the same character hides in the same closet. But it all feels natural, even inevitable — at its heart, this story is largely a 16th-century romantic farce.
* If your central character trait is "good at business and organization", and you are a fictional character, you are almost always a villain. This is less common in manga, but still prevalent. It's nice to read a story where the good organizers are also good people, with the same good traits motivating both qualities (hardworking, creative, attentive to the feelings of those around them).
The main character is a womanizing power fantasy Gary Stu, but also such a hapless goofball that I didn't really mind. Aside from that, and a few scenes involving the various racial/sexual stereotypes of the 1980s, this is a very well-told slice-of-life story.