Deemo: Prelude  

“Never left without saying goodbye.” A girl who lost her way and found herself in that mysterious place met “Deemo,” a man dressed completely in black. There, every time they played the piano a tree would grow taller, leading them to the “place” where the girl would have to return. And then, the “dream” that both the girl and Deemo wished for at the end is―Source: MU

Deemo: Prelude is a prologue of Rayark's 2013 video game Deemo for mobile.