So MC's sister wrote a novel because she recieved some kind of massage telling her what is going to happen in two years. She had to let the world know, but in an indirect way. Everyone became ~2.0 cm tall, in return for their height loss, everyone gained an ability. MC had the title "Prince" and the ability barrier. Thats basically all I remember. I think his sister was also trapped by a a person with the ability to enlarge themselves.