Junpei is usually portrayed as goofy, perverted, immature and upbeat. He fancies himself a ladies' man and frequently tries to hit on girls, with little to no success. Despite this, he is capable of being kind and caring, and he often cracks jokes and calls people "dude" to make them feel better.

Later, it is revealed that Junpei's 'class clown' persona is largely a facade to hide his deep insecurities; as far as he's concerned, fighting is the only thing he's ever been good at, and he hates that there's someone better than him at even that (the protagonist). It's because of this that he is initially annoyed that Tartarus and the Dark Hour would soon be gone, as that would mean taking away his purpose in life. Sometimes, he is shown to be upset, depressed or angry as a result of his father's alcoholism, whom he resents and has a poor relationship with. Besides these displays of negativity, however, Junpei's attitude usually remains carefree and lighthearted, and he rarely shows his true feelings in the presence of his friends.