Well in the trailer, Terra is running from the light that turned into darkness; and Ven is running from the darknees that turned into light(I think so at least). This must mean that Terra is trying to run from the darkness instead of accepting it like MX wants him to(sorta like Riku in Re:Com). And Ven well now thats a mystery but I can assure u that it has something to do with Vanitas I just know it has to be.....well thats my theory.