Official art of Antimony at his computer (Source)
Antimony is a metallic element having two forms: a hard, extremely brittle, lustrous, bluish-white, crystalline material and a gray formless type.
Antimony (sometimes called Ant for short) is the protagonist of circuitdream.exe.
Animony has messy, dark greyish-blue hair. He wears a grey-blue jacket with a yellow border and a black shirt underneath. He wears red-tinted shades, along with white shoes.
Judging by the story being based around Antimony trying to find out why his brother is in the hospital, it can be inferred that Antimony is a caring person.