I was given another chance to give a happy ending in another world

Kamiya Rei a child that seeks knowledge because of curiosity. As he lives on the earth he encounters many problems. As he was slowly drained by the problems he encountered a girl who is also suffering. He was questioned, "Do you believe in a world of a happy ending?". As he wants to give a happy ending he realizes his helplessness. Now he is in another world can he give a world of a happy ending for the people he loves?