Yamashita Kazuo starts as a timid, average person who is pushed around by the manager in his company ( "Nobi Publishing" ) and by other people in general. However, after meeting Ouma and being exposed to blood lust and other fighters in the Kengan world, he started to lose his fear of ordinary people such as his manager and even to thugs who threaten to kill him. During the Kengan Annihilation Tournament, Yamashita becomes much more brave and respected.

By the end of Kengan Ashura Kazuo becomes the CEO of Yamashita Trading Co.

In Kengan Omega, Kazuo's company takes a new role of taking in freelance fighters under the order of Hideki Nogi, the chairman of the Kengan Asociation.

Trivia:
1.He has a wife and two sons. However, his wife left him 10 years before the story began.
2.Yamashita had been employed at Nogi Publishing for 34 years.
3.He enjoys watching martial arts and living a peaceful life.
4.Yamshita's motto is, "Good can come out of misfortune".