What is it?
The 1999 anime TV show Now And Then Here And There.
Here is how Wikipedia describes this anime TV show:
Now and Then, Here and There (今、そこにいる僕, Ima, Soko ni Iru Boku) is a Japanese anime television series conceived and directed by Akitaro Daichi, with a screenplay by Hideyuki Kurata. It premiered in Japan on the WOWOW television station on October 14, 1999, and ran until January 20, 2000. It was licensed for Region 1 DVD English language release by Central Park Media under their US Manga Corps label. Following the 2009 bankruptcy and liquidation of Central Park Media, ADV Films rescued the series for a box set re-release on July 7, 2009. However, the ADV re-release is now out of print. The series is available for purchase through iTunes, YouTube and Google Play.
Now and Then, Here and There follows a young boy named Shuzo “Shu” Matsutani who, in an attempt to save an unknown girl, is transported to another world which may be the Earth in the far future. The world is desolate and militarized, survival is a daily struggle for displaced refugees, and water is a scarce commodity.