This study investigated the effects of (a) the amount of pleasure reading completed, (b) the type of texts read (i.e., simplified or unsimplified books), and (c) the level of simplified texts read by 14 Japanese university students who made the largest reading rate gains over one academic year. The findings indicated that the participants who made the greatest fluency gains read an average of 208,607 standard words and primarily read simplified texts up to the 1,600-headword level. This study also provides an empirically supported criterion for the minimum amount learners should read annually (i.e., 200,000 standard words), provides direct evidence that simplified texts are more effective than unsimplified texts for reading rate development, and is the first study to provide empirical evidence that reading lower-level simplified texts within learners' linguistic competence is effective for developing the reading rates of Japanese learners at a lower-intermediate reading proficiency level.