@kronix she used talk no jutsu and the power of friendship on a sentient weapon, so that the weapon would betray its master and self destruct itself killing the dungeon boss in the process.
I wonder if this chapter is a reference to the Amorphis song. It makes reference to solitude and forging (not to mention the band have been referenced before).
@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.
Like I said about the dragon's backstory: if the author makes this kind of backrounds for joke characters, I can only imagine what is in hand for Noah's past...