@MacMeaties
This is Narita Imomushi we're talking about; of course it's the Amorphis song. Amorphis is one of his favorite bands and has already referenced it once or twice in previous chapters, with one spell straightup being call "Amorphis". The spell this chapter was called
Sacrifice and Riff called the charm at the end
Sampo, while the chapter title itself is
Skyforger. I can only assume he was listening to Amorphis while writing this chapter.