That was a cool one do dig in details with such a small piece of paper to work with :)
I used a 400g/m² paper, graphite (carpenter HB flat lead pencil for draft, 2B flat lead mechanical pen to lay out first details. I love these flat leads pencils for traditional work ), then inked it with 0.3 to 0.05mm inkpens and finished that with cold/warm grey promarker tones :)
Also part of the gift I did to my beloved one ♥