Johnson, Jadon (TTh) Now and Then, Here and There 50

Now and Then, Here and There (1999) is a dystopian sci-fi adventure anime about a young boy, Shu, who, after getting involved with a mysterious girl named Lala-Ru, is transported to a desolate world on the verge of solar annihilation. Lala-Ru and Shu are imprisoned at Heliwood; a mangled techno-fortress run by a megalomaniacal despot who commands an army of unwilling child soldiers. Shu and Lala-Ru struggle to escape the clutches of Heliwood and put an end to the one-sided war that plagues the already doomed desert. The series is available on Amazon Prime Video, in English.

Here's the link to a 1-minute trailer:
https://youtu.be/BsYY0ReMGz0