Good thing the Outrunner is a hybrid so that it can make menacing engine noises when it needs to (though I guess they were just mostly flashing the lights).
I wonder who the destroyer godkin is and I'm guessing he might meet them. I think Out probably isn't the destroyer; he doesn't have any magic circuit and his ability is basically to trigger the Outrunner's magic circle to travel through time and worlds. On the other hand, we've learned that humans from his world are compatible with magic, namely Miya, and that they can be quite talented, apparently. I'm quite sure Miya has every intention to keep coming back and to learn magic so she might actually be the person Nimbus is referring to.
I'm curious how he'll solve the aging issue; as he's stated, he'll appear to be aging faster in his world due to spending extra time in otherworlds. Considering he can time travel, I wouldn't be surprised if his time was frozen in some way while in the other world, or maybe magic can somehow restore youth. Azu has been shown to have some capability of analysing the Outrunner's magic, and will apparently achieve other things which will help Out in his journey, such as the book.