It is a passport size MD paper cream refill.
"MD paper" is an original writing paper that was developed in pursuit of ease of writing, making it difficult for a fountain pen to bleed or fall through. White is used in the standard "no-scoring" and "horizontal-scoring" but this is cream MD paper. The cream-colored paper that feels warm and gentle to the eyes also reflects the blue-black color of the fountain pen.
MADE IN JAPAN