Ok, as someone who grew up around art like this on shirts for sportsman drag racers and local short track drivers to sling on T shirts to break even on their hobby or career, it's huge a surprise to see on here.
The calligraphy is a reference from The Ballad of Changgan, by Li Bai. Where the idea of childhood sweethearts/青梅竹馬/幼馴染(Osananajimi), in Chinese and Japanese culture originated from.