My idea for the contest is Day and Night. They appear everyday but was never meant to meet each other. I guess you may also look at this as Fire and Water :/
I wish I can make one more entry but I have a final project with dateline apporaching lol. Okay, gotta run again
It reminds me of the story Ladyhawk c: The man is a man by night and a bear by day and the woman is a lady by day and a hawk by night. Or something like that. And the only time they can ever see each other is when they're in a cave and one is covered in shadow and the other in sunlight c: