Tonelico no Ou

When Shiro, who had been sleeping in a giant tree, wakes up, he finds himself in a new world where nuclear weapons, global warming, and energy problems have been eliminated. It is a future ruled by the “World Tree". A girl with sky-blue hair tells Shiro that he is a survivor of the previous era. He is bewildered, but soon comes to understand and adapt to this new world of the future, where androids serve humans, and where common sense is a rarity. As the days become peaceful and boring, Shiro's memories of his past life begin to fade...
In this futuristic fantasy, ideals, reality, and the value of one's own existence are revealed.

(Source: Hero Bunko, translated)