Before The Mad Capsule Markets, there was a band named Berrie. Before Berrie, there were a group of kids growing up listening to domestic and international pop and punk rock, learning to play instruments and rock hard.
Kyono and Shin started a BO0WY copy band in high school; their first performance was their senior year at a school festival. BO0WY was an extremely popular rock band in Japan in the 80s. Masa, editor of the fan site "Mad Chuudoku [Madness]" makes a big deal about similarities between "Humanity" and "Moral", BO0WY's first album. He also points out several BO0WY songs that seem to be the inspirations for early Mad lyrics. He claims that the pseudo-nym for Kojima Minoru, Moruhime Shin, is a conglomeration of characters from the names of different BO0WY members.
Takeshi got interested in music afer being exposed to YMO. After getting into Stalin, he fell in love with 80s Japanese punk like Aburadako and INU.
In an interview, Kyono explained that he used to be an MTV junky during junior high. He doesn't even remember the bands that he liked watching most, just that they were new wave and punk. Kyono was in junior high from 1981 to 1983, so think about who had popular videos during that time. Kyono goes on to say that in high school he started listening to Japanese punk like Gauze, Starlin, Inu, and Aburadako. Then he ventured out into overseas punk like Crass and Pop Group.
In another interview, Kyono explains the formation of TMCM and its predecessors. Apparently Kyono and Shin were bored with the music that was playing on the radio and on TV. They wanted more loud, punk music, so they set out to make it themselves.
Focusing on their punk rock roots really doesn't explain the complexity of their later sound, though. For example, consider that Kyono's first CD was ELO's "Secret Message"
Some of this information comes from Mad Chuudoku (Mad Madness). If you can read Japanese, you should dig around in this site. Thanks to Masa for letting me steal from his content.