Nana has lost all the crayons to her store along with Monkichi! Each chapter title is based on the game Shiritori and the theme of the chapter is based on the title which helps Nana find her crayons and Monkichi.
Shiritori is a Japanese word-game which involves taking (tori) the syllable from the end (shiri) of a word, and thinking up a new word which starts with that syllable. One English name for this game is "word chain." If you want to try it out, you can even play online in English at http://shiritorigame.com/
In this manga, the dialogue itself doesn't use shiritori, but the chapter titles do. So the first chapter named "store" or "mi se" in Japanese, leads into a second chapter named "laundry," which is "se n ta ku" in Japanese.
