does this mean the demo is free but we have to pay for full game ?
Basically, yes. Creating this game takes a lot of time and effort, and though I develop the main bulk of the game myself, there are still things that need to be paid for (e.g. music), so unfortunately I cannot afford releasing the full game for free. I aim to keep pricing reasonable though, so don't worry. :3 Also, supporters on Patreon will receive their own free copy (I'm going to post more on this soon).