Don’t worry, your eyes are not playing tricks on you. There is no bun to this burger but the one you see made out of rice from a placed called MOS Burger.
MOS Burger (モスバーガー), (Japanese, “MOS” or “Mountain Ocean Sun”), is a fast-food restaurant chain that originated in Japan. It is now the second-largest fast-food franchise in Japan after McDonald’s. Personally, I think the food here tastes 10 times better than McDonald’s. One thing that is unique about this place is its rice burger. The MOS Rice Burger uses a bun made of rice mixed with barley and millet. Rice was first used as a bun in 1987, when the restaurant served the Tsukune Rice Burger, filled with ground chicken and daikon, and seasoned with soy sauce. Tsukune (つくね) is a japanese chicken meatball and personally one of my favorite meat selections in Japan.
The above burger you see is that very Tsukune Rice Burger which has finally made its reappearance after coming off the menu a while ago. I must admit that it was more of a hassle to eat than it was worth as the rice bun started falling apart, it was still delicious and I would not mind ordering it again.