Kazuma is a calm, serious, and sensible person. He cares greatly for Vaisravana/Bishamonten, calling her by a pet name, "Veena", as well as his fellow Shinki. He is also shown to be extremely loyal to his master, as well as responsible and trustworthy. He also honors his debts, particularly to Yato. He is polite to everyone, regardless of if he is stressed or not. When he was just starting out as a shinki, he was shown to have no talent but is currently a blessed shinki, meaning he is hardworking and his loyalty and care for Viina motivated him to be the best shinki he could. While loyal to his master, he is also loyal to Yato as he helped perform Yukine's ablution to save Yato and protected Yukine from Viina due to the fact he begged Yato to slay his fellow shinki to stop their blight from affecting her. He is a kind person in general and a good teacher, as he willingly teaches Yukine some techniques as his fellow blessed shinki. Despite his serious nature, he is shown to have a comical side. While using bind on Yukine to help him practice to use the technique and develop his defense, each time Yukine lost he drew on his face until he looked ridiculous. On another occasion, in chapter 40, when he and Yukine were practicing using shinki techniques, Yato mentioned how Kazuma had a horde of Bishamonten photos and admitted to supporting Yato since day one without feeling guilty, causing Viina to beat both Kazuma and Yato up. the fact that he has so many photos of her, even on his smartphone as mentioned in chapters 38 and 39, heavily implies he has feelings beyond a master and servant and that he holds her in a romantic regard but doesn't act on those feelings, possibly since he feels that would infringe upon their relationship as master and servant, her status as a God in contrast to his lower status as a shinki, and the fact that, as stated in chapter 7 of Noragami Shuushuu the seven gods of luck are not allowed to get themselves involved romantically.
In some ways he is somewhat similar to Bishamonten as he is shown to hate Nora like most characters of the series and as a result hated the idea of having to bow to a Nora to save his master (As Yato's only shinki at the time was Nora) just as how Viina hated Yato because he saved her twice and how she couldn't protect her two shinki clans and had to rely on a no name God to save her. He also admits he felt he is worthless because after asking Yato to slay the Ma clan, he was going to reveal his treachery to Bishamonten but when she told him she only needed him he felt a sort of happiness hearing that and decided to let her continue hating Yato so she could heal. He admits he felt good being needed and just wanted her to smile but after seeing the destruction she caused (influenced by Kuguha) he felt he failed as her blessed vessel because he made her upset a second time. He continues to think back to Bishamonten's first leads words when Kazuma was a nail about how Kazuma was a bad omen since he pierced Bishamonten's body, though Bishamonten assures him that she still wants him to follow her. He has even stated in episode 4 of Noragami Aragoto when he asked Yato to kill the ma clan that only Bishamonten owns his name and in chapter 25 when Ebisu tries to buy Kazuma saying it is alright if Kazuma is a stray because he values Kazuma's skills, Kazuma states the only one he wants to protect is Bishamonten, causing her to blush.
As someone who had to work hard on his abilities, even though he was just a simple nail, has since become a blessed vessel and one of Bishamonten's battle shinki. He is very knowledgeable about his duties as a shinki and about techniques to use as a blessed shinki, despite most likely not having a teacher. He mentions in chapter 27 how in order to use Bind you must first know the opponent's name, second consider yourself superior to your enemy, and third practice. He is very analytical of Viina's battle situations and does his best to guide everyone to make sure they can help Viina to the best of their abilities. He was even able to help Viina defeat one of the toughest non blessed shinki (it is unknown how many blessed shinki there are but it is implied in chapter 58 that Yukine, Kazuma, and the sealed hafuri are the only ones in heaven) though they still couldn't save Ebisu from heaven's wrath. According to him in chapters 35 and 40, this is because , as he has stated "to be in total control of a situation, you must have confidence in yourself". In his practice fight against Yukine, when Yukine calls him Kazuma-san Kazuma thinks to himself Yukine has already lost because by calling him san he acknowledges Kazuma as his superior and since he can't win a battle by acknowledging his opponent as superior he has lost. Despite showing pride in his abilities, he is not arrogant about them and does his best to continue improving himself for Bishamonten's sake.
In order not to blight his master, he is shown to suppress his feelings and not feel guilt for his actions, no matter what they be. In chapter 40, when Yato revealed Kazuma supported him from day one Kazuma readily admits it, saying it was because Yato was their benefactor and therefore what he did wasn't wrong, and it was shown Bishamonten didn't get stung, though she was annoyed. He tells Yukine this is because if he does not feel guilt for his actions then what he does is not a sin and will not blight his master and how Yukine should see Yato as his top priority, showing a colder, darker side to his personality. He evens states that he is not perfect and has regrets but felt he did the right thing and so it was not a sin and doesn't warrant anyone's criticism, something Yukine found to be extreme. His loyalty to Bishamonten can go to extremes as he was willing to slay his fellow shinki to save her and after the sorcerer Fujisaki infected Tsuguha and led her to receive her memories and turn ayakashi, he coldly slayed her to save Bishamonten but didn't blight her because he didn't feel guilty even though she was his friend and ally because he believed he did the right thing. He also used bind on Yukine to force him to reveal the location of the sorcerer, despite knowing doing so would endanger Yato's health, breaking off his good relationship with Yukine who now considers him an enemy.