"Tegami (Haikei Jūgo no Kimi e)" (手紙 ～拝啓 十五の君へ～, "Letter: Greetings to a 15 Year Old") is the eighth Japanese single by Angela Aki and was released on September 17, 2008. It was broadcast in a music program Minna no Uta in August 2008 with some re-runs. The song reached number three on the Oricon Weekly Charts, selling more than 200,000 copies. It was certified Million for downloads in 2016 by the RIAJ.^[1] The song is performed in the anime movie Colorful.

The song was ranked at 25 on "Billboard Japan Hot 100 Songs" chart.^[2]

The B-side "Still Fighting It" is a Japanese language cover of Ben Folds' song of the same name. Aki herself wrote the Japanese version's lyrics. Folds himself, by chance, heard Aki cover the song at the 2008 Fuji Rock Festival. He was impressed, and met with Aki. Due to this, they collaborated on the song "Black Glasses", on Aki's next album, Answer.^[3]

The song is the self-cover of the choir song Angela originally wrote by a request of NHK, the national public broadcaster, as the compulsory song in the 75th NHK National School Music Contest in 2008, Junior High School (12–15 years old) Division.^[4] Arranged by Hiroaki Takaha, the girls' and mixed demonstration choirs were broadcast in March 2008.^[5]

This song has also been sung by Taiwanese singer Rene Liu under the title "Strive On: To My 15 Years Old Self (Chinese: 繼續~給十五歲的自己~). Chinese singer Chen Ming (陈明) under the title Letter (信), Bibi Zhou under the title Write to Future Myself (写给未来的自己), Hong Kong singer Sherman Chung under the title Letter to Myself (給自己的信) and the 15-year-old Japanese singer and Morning Musume member Mei Yamazaki.^[6]