He has messy, bright red hair and similarly colored eyes. He normally wears his uniform in a casual manner, which he doesn't wear too loose or too neatly.
Otoya is an energetic yet a gentle young man. He is nice to everyone no matter who they are and loves music more than anything. He's a kind, bubbly, and light spirited character.
Fifteen years ago, his mother supposedly died in a plane crash, resulting in him having to be brought in at an orphanage. Also, he has never "met" his father, who is in fact Shining Saotome. His adoptive mother, who is a Christian, also gave him a rosary that he keeps with him. It is later revealed that Otoya's mother is in fact alive and well, though suffering from amnesia.
In the fourth season of the anime, it was revealed that he was adopted by his maternal aunt after his mother's disappearance. However, his aunt had frail health and soon succumbed to her illness when Otoya was still young. This emotionally scarred Otoya who became scared that he would easily lose anyone or anything who were closest to him. He was eventually able to move forward from his past, until Eiichi brought them up for the sake of the duet project. This mentally broke Otoya who became convinced that he had been deceiving everyone by using his smiles to hide his emotional scars, and that ST☆RISH and Haruka would leave him should they learn the truth.
Haruka's classmate in A Class. He's a friendly and positive person who enjoys singing. He shares a room with Tokiya from Class S. In the anime, he stands up for Haruka when she was barred from taking the entrance exam due to being late. He enters the Academy partly because "singing seemed fun and interesting" but after meeting Haruka & hearing one of her songs, he falls in love with her caring, hard-working and "never-give-up" personality and starts to pursue becoming an idol seriously. He is somewhat intimidated by Tokiya since the beginning because of his "perfect singing".
They first met when Otoya defended Haruka's right to enter the entrance exam with Ren. Later on, they found out they were in the same class. Haruka was Otoya's partner in their first assignment in the school. Since Haruka didn't know how to read music, he encouraged her to do her best about it. Otoya couldn't come up with the lyrics even after consulting the other guys for tips. It wasn't until he heard Haruka humming a theme that he finally got inspiration. They created the song "Brand New Melody", and they both passed with high scores. In episode 8, Otoya confessed that he loved Haruka's music, and was going to request her as his partner for the graduation audition. In the end, he was in the group ST☆RISH with the other five people who also requested Haruka to be their partner.
Tokiya is Otoya's roommate. He's the complete opposite of Otoya and seems to find his roommate a bit bothersome at times. Tokiya is a calm perfectionist, whereas Otoya is very childish. Tokiya gives him pointers about how to come up with lyrics (reluctantly), even though Otoya has a hard time understanding him. However, over time, their relationship begins to loosen up.
Cecil is a friend and band-mate of Otoya. The two get along pretty well, Otoya was one of the few that was immediately friendly with Cecil when he first arrived, but he doesn't like his romantic advances towards Nanami, like the rest of STARISH. He indirectly helped Cecil want to become an idol when the two worked on a TV show together. Otoya was also one of the first few to say that Cecil should join STARISH after they all sang together and was thrilled that he joined, he also pleaded with Saotome with the rest of STARISH to allow Cecil to join, which worked after they performed for him. It's later revealed in the games that the two are half-brothers, the two born from the same mother, but different fathers; this has not yet been established in the anime.
The official website for the anime confirmed his age to be 15. However, since his birthday is in April (April 11th), not long after a Japanese school year begins (April1st), should the series' school system be based on Japan's, he'd age right after the beginning of the school year to 16. In comparison, Syo's birthday (the date of which he also shares with Natsuki - June 9th) follows Otoya's; meaning Syo would age after him, but not long after as well. This would also apply to Cecil, whose birthday is October 31st, also coming after April; and possibly Haruka, noted to be the same age as Otoya and Syo (though she is not given an official birthdate). (If Haruka were the same age as both of them, based on a real world system, this would place her birthday after April 1st, and possibly before Syo's June 9th.)
Just like all the members of ST☆RISH, he has a designated theme color. For Otoya, it is red.
His given name, Otoya (音也), contains the Japanese character for sound (音).
His last name, Ittoki, contains the characters, 一 (one), 十 (ten), and 木 (tree).
In the game, he is the one with acrophobia, unlike in the anime, where Kurusu Syo is the one afflicted.
Even though he has a rosary, he states that he is not a Catholic.
In Debut, he revealed that he now knows that Shining Saotome is actually his father and that he is a child out of wedlock. 
Otoya is seen to be very acrobatic, along with Syo.
In the Radio Drama for All Star, Otoya states that he enjoys soccer, using the balance ball, and the lifting test in soccer.
He shows no preference between summer (warm months) and winter (cold months).
His favorite food is curry, but he dislikes green peppers and black coffee.