Tenmon (天門?), born Atsushi Shirakawa (白川 篤史 Shirakawa Atsushi?), is a Japanese music composer from Tokyo, Japan born in 1971. He worked in the Nihon Falcom Corporation as one of the members of Falcom Sound Team J.D.K.. During his time with Falcom, he has composed much music for Falcom games, most notably Brandish.
Having known Makoto Shinkai as a coworker in Minori he has composed music for Shinkai's works since She and Her Cat. He is perhaps best known for creating the soundtracks for Shinkai's subsequent works, Voices of a Distant Star, The Place Promised in Our Early Days, 5 Centimeters Per Second and Children Who Chase Lost Voices from Deep Below.
In 2009, an album, titled "Promise" ("新海誠作品イメージアルバム「Promise」"), performed by the Eminence Symphony Orchestra, based in Sydney, Australia, was released, celebrating ten years of collaboration between Tenmon and Makoto Shinkai. It consists of orchestral arrangements of a variety of pieces composed by Tenmon appearing in a range of Makoto Shinkai's works. 
Tenmon has composed the soundtrack for:
- She and Her Cat (1999)
- Voices of a Distant Star (2001)
- Mizu no Kakera (2001)
- Tenshi no Kakera (2003)
- Haru no Ashioto (2004)
- The Place Promised in Our Early Days (2004)
- Ef: A Fairy Tale of the Two. (2006)
- 5 Centimeters Per Second (2007)
- Ef: A Tale of Memories. (2007)
- Ef: A Tale of Melodies. (2008)
- Eden* They Were Only Two, On The Planet (2009)
- Children Who Chase Lost Voices from Deep Below (2011)
His other works include an original album Chronicle released in 2012.
- "Official Project Promise Website". Retrieved 2010-03-31.
- "Eminence Presents: Project Promise – 10 Years of Makoto Shinkai & Tenmon". Retrieved 2010-03-31.
- "Makoto Shinkai x Tenmon 10th Anniversary Orchestral Album". Retrieved 2010-03-31.