The checkered pen is "Checkerpen-α" (Alpha).
The Secret of Checkered Alpha
There is a reason to achieve a beautiful finish.
Reason 1: "Bright color" / so it is easy to read.
Reason 2: "Does not bleed through the back" so it is clean and easy to read.
Reason 3: The "bold" tip has a tight nib, so it fits perfectly on both flat and curved surfaces. It is easy to draw lines on curved surfaces such as thick dictionaries.
Cannot be erased with a check-off pen.
Blue ink is hidden in red sheet.