Itsuki Kawasumi/Relationships

Naofumi Iwatani
Itsuki looked down on Naofumi because he considered him to have the weakest weapon. Because he was easily gullible, he believed Malty's accusation that Naofumi attempted to rape her and berated Naofumi without hearing or believing his side of the story. He readily believed Naofumi was guilty of stealing his achievements even without evidence to back up that belief and still tried to insist it was true even when it was proven otherwise. He believes Naofumi to be an evil person and readily accepted any accusations made against him without question, such as Naofumi brainwashing the people and kidnapping the second princess.

After Naofumi's name was cleared, he agreed to the queen's idea of giving a little preferential treatment to Naofumi, in-order to balance all the past misdeeds against Naofumi, but Naofumi felt he was just saying that for show and was sure that he would throw a tantrum. Itsuki doesn't like the idea that Naofumi is more powerful than he is in general but more specifically because he feels that Naofumi's job (The Shield Hero) should be weaker than his own and felt him to be bossing him & other heroes. He openly accused Naofumi of cheating to try and outshine him. This directly led to his involvement in the spirit tortoise incident.

Likewise, Naofumi didn't view Itsuki in good light for he sees Itsuki as a self-centered, approval seeking person. However, what little respect he had for Itsuki completely disappeared when Itsuki kicked Rishia out of his party for being weak.

Despite all that, Itsuki stood up for Naofumi after the rigged duel when he pointed out Malty's involvement in it. He also demanded to know the reason for revoking Naofumi's payment as he didn't get any job from the guild to support himself.

Ren Amaki
Itsuki along with Ren and Motoyasu fought the wave bosses. Ren was also able to reason with Itsuki about how there was little to no evidence of pinning Naofumi of stealing Itsuki's accomplishment. Though he firmly believes Naofumi to be a villain, Itsuki was willing to listen to Ren's suggestion of investigating the back story of the kidnapping incident, to see if Naofumi was really telling the truth.

This shows a certain degree of trust between them. Despite fighting alongside him, Itsuki was just as surprised as Naofumi after leaning Ren's way of working with his comrades.

Motoyasu Kitamura
Itsuki was a little envious of Motoyasu's preferential treatment. Itsuki along with Ren and Motoyasu fought the waves and the final bosses. Itsuki along with Ren called out Motoyasu on his rigged duel with Naofumi. Motoyasu considered Ituski and Ren as his buddies and went on a rampage against Naofumi after being falsely informed of Naofumi's involvement in their deaths. Later, he joins with Naofumi to fight against the Pope for the same reason and vows to avenge them and give them a proper funeral, but is surprised when they turn out to be alive.

Glass
Glass defeats Itsuki with great ease, believing him to be a normal adventurer and wonders aloud where the other heroes are. While She acknowledges Naofumi alone to be a hero.

Rishia
Itsuki rescued Rishia from an evil Noble man. From then on Rishia follows Itsuki obeying his orders to the letter, though she was mostly mistreated by her fellow peers. Rishia mostly reminded Itsuki of himself from his original world and tried to bury it. Itsuki and his comrades forced her to focus on her weak points rather than sharpening her strong skills. Itsuki finally snapped when Rishia received praise from the queen for being useful in handling L'arc while he wasn't. Because of that he framed her and kicked her out. When questioned as to why by Naofumi, he replied that she was too weak and did it for her own good, which pushed her to try and commit suicide. Later, Risha grows strong under Naofumi.