To recap what has already been said:
1: I have another soul with me.
2: I call upon him whenever I'm in trouble.
3: I live with my Grandpa.
4: I may look small, but I'm in high school.
5: I had no friends until one night when I completed a puzzle.
6: I've won many competitions around the world.
7: I value friendship more than anything even more then winning.
8: The puzzle I completed, I wear around my neck.
Now for 2 more clues:
9: I like to associate myself with magicians and gods.
10: My main rival is a billionaire who owns his own company.
Avatar: Kurumi from Date A Live