It's actually the second part of the series. I didn't want to write this one first because it would spoil the first part... But I don't want to write the first part now. I really like that one so I practice my writing first.
By the way, the first chapter is an introduction, which does not affect the plot. It's just that I wrote it crookedly when I wrote it. I'm reluctant to delete it but it's also inconvenient to post it...