Most particle production can be solved by approximate methods, but some problems cannot be solved without serious consideration of the Stokes phenomenon. One such particle production is baryon number production from rotating fields. Processes such as particle-antiparticle mixing increase the order of the differential equations to be solved, so new knowledge of ExactWKB, including Virtual Turning Point, is required. The other is particle production from a steady state. This problem includes the Schwinger effect, the Unruh effect and Hawking radiation. In particular, the Stokes phenomenon of the Unruh effect has been unsolved for 50 years. This talk shows how the Exact WKB can be used to solve these problems clearly.