Mirai Shounen Konan
(Conan, The Boy of the Future)
From the prologue, in English, printed on the front cover of the LD version:
July 2008. Mankind was faced with the thread of extinction. An ultra-magnetic weapon, far more devastating than any nuclear weapon known, had destroyed half the world in a single instant. The earth's crust was rocked by massive movements, the earth was thrown of its axis, and the five continents were torn completely apart and sank deep below the sea...
The attempt by a number of people to free [sic] to outer space failed. Their spaceships were forced back to the earth and vanished with their hopes shattered.
But one of the spaceships narrowly escaped destruction and crashlanded on a small island which had miraculously survived the devastation. The crew members of the spaceship settled there, as if they were seeds sown on the island.
After years, a boy was born. He was a new life in the desert, a ray of light in the darkness of the annihilated earth...
And there this story begins.