It is oddly noteworthy that the Ethereal Dagger is classed as Armor Piercing by default, which is not a very common type to be a basic attack, and it's also been one of Edwin/Stargazer's weaknesses since the start, which is why it's always so hard to hit this thing effectively in early/mid-game.
When you think about it, this weapon being super effective against Stargazer is an interesting, indirect way for Spine to personally avenge her previous life (despite enjoying what she is now)...










