Despite what rumors you may have heard TK is not influenced by Number Girl nor Progressive Rock or Hardcore bands. Though TK's music is very complex his influences are in reality as follows:
Piano-based songs of which TK only likes harmonic songs (he calls them melodic songs).
He actually played the piano first before he began playing the guitar.
He is influenced by his father (Folk musician), Folk songs, J-Pop, and popular songs from Japan from the 1970s to 1990s by Kazumasa Oda, Kosetsu Minami, Miyuki Nakajima, Chiharu Matsuyama, Tatsuro Yamashita, and the Southern All Stars.
As he got older he began listening to LUNA SEA, B'z, GLAY, L'Arc ~en~Ciel, Mr. Children, Tetsuya Komuro, Takeshi Kobayashi, and Tsunku-san.
Lastly, memorable Western music he listened to while growing up is The Beatles and the Carpenters.
Source: TK's book Yureru, With J-Pop