1.You Can Use "Black Pen" for the "Disappearing Pen Refills". Please Just Replace the Black Ink Cartridge in the "Black Pen" 2. Please Just Replace the Black Ink Cartridge in the " Carrot & Elk Pen" with the "Blue Disappearing Ink Pen Refill". 3. You can Use a Empty Pen Case Directly for "Blue Disappearing Ink Pen Refill" , Just Enjoy 1 Pen Grip!!!