It's not real but does exist, it helps to determine where a plane will drift, you'll see it in math but never on a ruler, and it was first annotated by a man named Euler

You always find me in the past. I am made in the present, but in the future I am nothing. What am I?

I live in the past but visit today, I color memories in a gentle way. I whisper of things that made you smile, And take you back for just a while. What am I?

I am old, but not alive; I tell a story, though I cannot speak. I am found by digging, or in a special home, revealing the past with every piece. What am I?

I used to be part of a powerful symbol. I am also the name of fictional ninja. I can be made into jewelery and figurines.