|“||Huh? Why am I crying? Rishia... I'm sorry... for everything.||”|
—Itsuki, Volume 12, Chapter 13
Itsuki has short light brown curly hair and dull golden eyes due to the effects of his curse series.
He appears to primarily wear a sleeveless tunic with light clothing underneath. Additionally, he wears thin leather gloves, leather boots, and a green hood-like cape attached around his neck and right shoulder.
The weapon in his possession is the Legendary Bow which was granted to him when he was summoned to another world.
Itsuki feels in his own mind that he's the strongest of the Heroes, and undergoes stealthy missions to kill corrupt nobles and save villages, almost always just for the praise. Being a bullied child has left Itsuki with a desire to be special and superior. His sense of justice and need for praise both stem from this, as does his inability to deal with the meek Rishia Ivyred, who reminds him of his weakness.
Like the other heroes, Naofumi Iwatani excluded, Itsuki believed that the world they had come into was identical to that of a video game, but he goes further than they do and believes Naofumi has met God, i.e. the game master, and received powers from him to explain his superiority. Even after becoming a yes man and having everything shattered, he still feels that the fact that Rishia is stronger than him has to be a cheat. He also thought he was immortal since the "game" wouldn't let him die.
He called himself an ally of justice and tried to act on it, at least at the beginning. But, he lost the true essence of justice and instead just acted on his own selfish desires of getting praised, under the guise of justice. His sense of justice was so overpowering that he refused to listen to what anyone had to say and believed his own to be the only true justice. Though he goes on about justice on a regular basis, his view of it is incredibly self-indulgent and one-sided. He was willing to put everyone he believed to be evildoers to death just because he believed they were evil and was willing to kill them. This got worse when he was affected by the Curse Series.
He can also be quite gullible and unobservant, though not to Motoyasu Kitamura's extent, as all of his teammates excluding Rishia are in fact extremely untrustworthy people who just praise him all the time. They just fed his desire to be praised and every time they did, he felt satisfied by their praise. Then again, he can be easily fooled like he was by the Church of the Three Heroes when they lied about Naofumi's misdeeds and that Naofumi had an item that supposedly had the power to raise his EXP intake. After awakening his curse series, he believed Naofumi was evil for having slaves and turning away people who he could supposedly revive from the dead because Malty S Melromarc tricked him into thinking the latter was possible. He believed those who praise him and not others who tried to reason with him.
He has a hero complex which means he will wait until people are in a crisis before acting so he can "save" them in a heroic fashion, going far enough to lie about his abilities to cover up his inaction before people fall into critical situations. He's extremely petty, and not very smart, believing Naofumi is guilty of both the false attempt of rape charge and later of trying to take credit for things he had done, which wouldn't be hard for anyone to do because Itsuki tries to be a robin-hood-esque hero who conceals his own activities often. His pettiness was once again exposed when Rishia was praised over him for her efforts against L'Arc Berg. To get back at her, he framed Rishia for breaking an item and kicked her out of his party.
In short, he's stuck up, gullible, and wants to be praised by others. The one thing Naofumi ever said to him that genuinely enraged Itsuki was simply "I thought you were better than this, my evaluation of you has dropped," for which he was willing to go so far as to shoot the Shield Hero in the back of the head.
After going through the events with the Pride Series and experiencing Malty's manipulation, Itsuki's prideful personality destabilizes and he becomes completely despondent. He now follows Naofumi's orders without argument.
Before being summoned into the world where the story takes place, Itsuki lived in an alternate world to our own, where some individuals were born with various supernatural-like abilities. Itsuki was born with the supernatural ability "Accuracy", meaning any ranged shot of a weapon or device he fired would - if not blocked - hit its target. As such, he was admitted to a high school designed for children with abilities.
Due to his experiences in middle school, which he spent in a regular class with people without abilities, he had developed an impression that he was particularly special due to his ability. However, his ego plummeted upon entry to the high school as he found he was classed among the weakest of those with abilities. Due to his supposed weak ability, he was bullied throughout his school years and turned to console games to escape reality. On his way home from prep school, he was suddenly hit by a speeding truck with no warning. He later found himself summoned to another world as one of the 4 Legendary Heroes, The Bow Hero.
- The name Itsuki means "tree" (樹).
- Itsuki's surname Kawasumi means "river, stream" (川) (kawa) and "clear, pure" (澄) (sumi).
- According to Itsuki, this world is similar to the console game known as Dimension Wave, but he was the first to agree that there is some difference.
- Apparently, Spider-Man doesn't exist in his world; despite making the famous "with great power comes great responsibility" line.