I've always thought there is only 1 type of light novel for this series (which is translated to other languages).
But I saw on Amazon that they are offering to sell 3 types of the same light novel.
You can see that below the title section, where it says "See all 3 formats and editions". After that, you need to press the arrow on the left side to see all the 3 novels.
I'm wondering what are the differences between them.