This includes the Miya? I hate to sound silly with this question, after all it is a MG?
Yes. This includes Miya and Miya Argento. Using some soap water might help. Dry ebonite feeds can be very tight sometimes.
Hold firm using your hand on the front and back sides of the nib and ink feeder then pull in axcial direction.
If it doesn't move at all, try sink the unscrewed section in warm soap water.
Always attach the pen body when unplugging the nib(for better gripping) and detach it when cleaning. Celluloide can react with some solvents and softens in warm water.
And if you could not pull it out. Try it later. The fins on MG ebonite feed are much stronger comparing to other brands, but they're not unbreakable.