I already guessed e as ruler but I bet shes lost her memory somehow and they used to know each other .
Otherwise how could the cafe guy remember her as his girlfriend.
I think he was dreaming of her then saw her and kept .. well dreaming lol
I think he was so surprised about the watermelon because her personality stayed the same after whatever memory wipe.
Because the world setting implies some kind of cyberpunk post apocalyptic world I feel comfortable assuming this