There are a few reasons we say that one of these concepts has to be the next Mazda3. One is the fact that Mazda says it's a concept planned for production. The company also describes it as "a compact hatchback that fuses next-generation technology and design," and it uses the new Skyactiv-X spark-controlled compression ignition engine and "Skyactiv-Vehicle Architecture." Plus, just looking at the teasers, the design is a clear evolution of the current Mazda3 hatchback. It looks as though the hood and roofline curve a bit more, and some of the sharp creases of the current car have been smoothed out.
The other concept Mazda is bringing to the Tokyo Motor Show seems to be just that, a concept. Mazda says it's just a design concept meant to exhibit how other Mazdas will look. Apparently it's a continuation of the company's current "Kodo" design language. Based on the teaser image, the car appears to be a sedan and consists mainly of clean, elegant curves, with hardly a crease anywhere except the edge of the trunk. The elegant lines are reminiscent of the RX-Vision concept, just with a couple extra doors and a different color.
Mazda will have a couple of other new vehicles on display in Tokyo as well. The company will show the Japan-only CX-8 three-row crossover and a special-edition Roadster (Miata) Red Top edition. We presume it's a Miata with a red soft top. Stay tuned for more details from the full reveal.