Although this seemed incredible—that a fictional world could actually exist—chakra was real. Since that was the case, how could the Naruto World not truly exist?
Bruce Banner might be just like the protagonists in novels from a certain Eastern country, having transmigrated to the Naruto World, where he gained the power of chakra and even acquired a method to pass chakra on to others.
After all, Bruce Banner was a scientist before this, and the Naruto World happened to have scientists too, like Orochimaru. In fact, the technological level of the Naruto World was quite high.
Chapter 174