He has messy black hair and seems to be rather tall. He wears a white shirt with a jacket and what seems to be jeans. They vary in color.
Arata has a rather easy-going and apathetic view of his future. He does think nor does he care about what he does with his life nor does he expect something from his life, instead of living fully in the present and leaving things to be as they happen.
Contrary to Yuki, however, he seems to be fairly more sociable as he does have a couple of good friends with whom he spends time often. The fact that his family was more stable than Yuki's prior to divorce may also contribute to his more outdrawn personality.
As soon as he's told about the game and its rules, he becomes afraid, but more for the people that dies around him than for himself, with his father's death having a strong impact on him, which moves him to do what's right refusing to go along the game's rules of murder, but fighting to save those who are around him in need.
Diary & Abilities
He owns the Perception Diary, it works similar to Yuki's Random Diary, it can predict everything he will see and hear, but little about himself, except from a Dead End entry which even then, is not as detailed.
Despite arguably having no past combat experience, he has proven himself to be a competent fighter with a bat. He has also demonstrated remarkable hand-to-hand fighting skills.