Which song exactly are you talking about? There are only 2 vocal tracks (the opening and ending) and over 25 instrumentals
Ah
finally someone appreciates this beauty ヽ(￣ω￣(。。 )ゝ saki_saki helped me out with the opening and ending, so let's give a big shoutout to her (and me!!!). Here's the link to the opening: opening.mp3
If you happen to like it so much that you want to listen to the rest, the entire music library from the novel (including the opening and ending by saki_saki) is available on Patreon for $2.5, and you can download it all. Plus, it's an awesome way to support the project |･ω･)