Every book includes four to seven stories or texts that progressively increase the level of difficulty and length.
This is the sixth volume. It corresponds to a level 6 (level 3-2 of the JLPT) and includes four stories. The first two stories are of an intermediate level (JLPT level 3-2) and the other two are pre-advanced level stories (JLPT level 2).
Each text is read out by a different voice which undoubtedly helps improve the student’s listening comprehension skills.
You will find the audios and some content samples in the links.
In the above image, you can look up the different levels.