Aneyama is one of the main antagonists of Riki-Oh, getting more screen time in the series than anyone else besides the titular character. A devout follower of Mukai, he goes out of his way to ensure Riki-Oh's capture to fulfill his plan to end the world, as well as his own twisted sexual desires. He quickly grows a massive hatred for Riki-Oh, and has him tortured once he defeats him in his first direct battle in the best way he knows how - making him watch as he kills innocents, powerless to do anything. Aneyama appears to be a young to middle aged man, but in reality he is over 80 years old. He makes use of his near infinite wealth and power to have monthly plastic surgeries and transplants of his failing vital organs. While he cannot fight directly, he makes use of a suit of high tech armor to greatly enhance his strength. His trump card is the ability to shoot bullets in such a pattern to sap all the strength of his enemies, as at this point in the series regular guns have little to no effect. Aneyama is ruthless and will kill his subordinates for mildly displeasing him in any way, such as by dropping a hair in his tea or referencing his old age. The only person he truly values is his dead sister, the only woman he ever loved, who's death drove him to be a homosexual. He is willing to tolerate his second in command, Dr. Kohinata, largely due to how competent and useful he is, having made his power armor for him as well as many other useful inventions. He still treats Kohinata terribly regardless, but he is the only one he will not kill for a small mistake. Aneyama is one of only two villains shown to have any direct contact with Mukai, and the other one, Washazaki, was fired in his brief contact with him. As such, Aneyama is Mukai's primary enforcer and voice, carrying out the majority of his plan, given Mukai's insanity and the fact he barely ever leaves his base in Antarctica.