After brainstorming many different ways to do unconventional drawing including sewing pills and pearls onto fabric and drawing 3D objects on papers, I finally decided to use stamp to draw a Kakashi portrait. The reason I chose a stamp as tool is that I was fascinated by an artist I met on the street. He only uses one single pattern to draw his entire drawing. I think the smart part is that when people look at his drawing from a distance, people can understand, "oh, that's a man's portrait". And when people walk close to his drawing, people will find that it's full of interesting details.
Kakashi is a character from a Japanese comic called Naruto. I like him so much, and I started drawing him when I was in middle school. I'm so familiar with his hair, eyes, etc. The picture below is Kakashi.
This is my tool.
This is a part of my drawing.
This is the final piece.
I like the final result, though I think I shouldn't add the red color, cause it feels inconsistent to other part of my drawing. I also think unconventional drawing is hard, cause it is difficult to control the tool and make ideal strokes. I feel like pencils and brushes are perfect for conventional drawing. But there are still many other possibilities.