Kazu is one of Takato's closest friends and is also a player of the DigiBattle Card Game, and there is nothing more Kazu enjoys than beating Takato and Kenta all the time. His involvement in Tamers truly started when Takato actually beat him, leaving him confused, but when Takato mentioned about real life experience, Kazu wanted to go deeper into it. When Kazu first saw Guilmon he and Kenta freaked out and ran away, but when he saw him as WarGrowlmon, he got to know what being a Tamer is all about. Kazu usually calls Takato "chumley" which shows how deep their relationship as friends are.
Kazu is known as the comic relief of Tamers due to the fact that he makes so many jokes and wisecracks to keep the entire episode amusing. He often does these jokes with Kenta and they make quite a pair. He's also had his share of one liners by himself, and with Guardromon, often ending up in mass confusion.
For Kazu, he may seem like just a comedian with no sense of purpose, but he is really a true friend and he will help out to the best of his abilities as he knows it's the right thing to do.
Digimon Tamers, 1st HalfEdit
Kazu proved how good a friend he was by giving Takato a Blue Card he made himself. He said that it should work since Guilmon came from a drawing, so why shouldn't this work. The card worked and it proved to be the one that saved the day. Secretly, Kazu wanted to be a Tamer himself and be just as good as Takato and the others. His chance came when he went to the Digital World, although he and Kenta did seem out of place as the others had Partners, he made the best of it until he did finally get a partner of his own in the name of Guardromon.
Digimon Tamers, 2nd HalfEdit
Kazu was the only one who stood by Guardromon's side when he was injured while the others went to rescue Jeri. The two became closer as Partner and Tamer, both in battle and in the multitude of jokes Kazu told, as Guardromon seemed to like to copy him (though Guardromon doesn't always understand; at one point, Kazu told Guardromon to watch Suzie, and when Suzie flew away, Guardromon said he "watched the whole thing", misinterpreting Kazu's meaning).
Kazu continues to demonstrate his capablilities as a tamer throughout the series, gaining the ability too Biomerge with Guardromon to form HiAndromon. While he has never proven absolutely essential for winning a battle, he has proven to be a useful assest none the less. He and his partner also managed to save a young boy, DC, from being hit and killed by a car (Kazu spotted it and Guardromon stopped it). This seemed to boost his confidence and ego further at least temporarily.
He also seems to have a complicated relationship with Ayaka Itou, a girl in his class. They seem to have a rivalry and even hate each other at times. But recent events seem to hint on a different emotion being stronger in their relationship. This was completely proven when he and Ayaka admitted their affection for one another and he saved her from falling to her death in the Digital World. While still new, they are already forming a close romantic ( at least, somewhat romantic...) foundation.