Aqua is the first person Kazuma meets after dying. Their relationship seems platonic thus far as neither of them see the other as an object of affection. That being said, they are inseparable and Aqua even relies on Kazuma more than she admits. He thinks she is useless yet cute when she is silent and calm. Despite their banters, they would save each other often enough, and she resurrects him whenever he dies.
Kazuma first refused Megumin's proposal to become a party member, because she could only use explosion magic once per day. However, he began to rely on her for the firepower needed to finish off monsters. Kazuma also carries her whenever she gets exhausted from using Explosion magic. Despite stating he is not interested in someone underage, he later showed some interest in her. This is most likely because she has finally entered his strike zone after turning 14, which is considered a legal adult in their world. When Megumin wanted to learn other spells so she could be useful to Kazuma, he stopped her and even buffed her Explosion skill because he knew she wouldn't be happy otherwise. He also sometimes get flustered by her actions, like holding hands when alone the same room. Kazuma has even been asked out by Megumin for a date, though it was just him accompanying her in casting a routine explosion spell.
Kazuma refused Darkness' initial approach to join the party but eventually conceded. While she fulfills his fetish of an "onee-san with great figure", her personality turns him off. Despite this, he often looks at her with lecherous eyes. Vanir teases that both Darkness and Kazuma have affection for each other but fear crossing the line of adventurer comrades, which greatly embrassed the both of them upon hearing this.
Chris is the first person to teach Kazuma skills. After he stole her panties, she starts wearing pants. He also respects her as his "big boss" and doesn't seem to mind forming a thieves' group with her, even if he would get in trouble with the kingdom for this action.
Kazuma regards Iris as the little sister that he has always dreamed of, a little sister who isn't bound by blood. In spite of initially disliking and underestimating him, she eventually warms up to the adventurer, causing of Kazuma's cunning and dirty tactics to rub off on her.