Limited availability of graded readers in Japanese highlights the urgent need for the development of reading materials to promote extensive reading in Japanese language education. To address this issue, we have developed new graded readers specifically designed for beginner-level learners. Through this process, we gained valuable insights into what it takes to create effective reading materials. In order to make the content easier to understand and more engaging for learners, we took into account the following factors: control of vocabulary and grammar, story content, number of characters, story flow and structure, background knowledge, and illustrations. In addition, we also considered obtaining permission from relevant individuals for the content of the stories, as well as the needs of readers with disabilities. Our findings will be useful for future development of graded readers.