Japanese rice, or japonica, is a short-grain variety of rice (Oryza sativa var. japonica) which is characterized by its unique stickiness and texture. The stickiness is necessary to eat it with chopsticks. Raw, not cooked rice is called kome (米) cooked gohan (ご飯) or meshi (飯). Gohan means a whole meal- this way you can see how important the rice is for Japanese people. The 2 main varieties are 粳米 uruchimai and 餅米 mochigome.

Hakumai

Uruchi-mai or uruchi-kome is a short grain variety, round or oval grains. Often you see Japanese rice called „sushi rice“, of course this kind can be used for all Japanese cooking, not only for sushi.
Most rice is sold as hakumai ("white rice"), with the outer portion of the grains (nuka) polished away. Unpolished rice (genmai) is considered less delicious by most people, but its popularity has been increasing recently because genmai is more nutritious and healthier than hakumai.
Popular varieties are koshihikari コシヒカリor nishiki. For example, Tamaki rice is a koshihikari, short grain rice. Other rice varieties close to its strains, such as Akitakomachi, Hitomebore, and Hinohikari have been created afterwards by cross-breeding Koshihikari with other Japanese varieties of rice.
Nishiki varieties are medium grain rice. Nishiki is a brand of California-grown rice, in Japan, some unrelated breeds of rice also have "Nishiki" in their names, such as Yamada Nishiki, which is used to brew sake.

Haigamai

Haigamai is short grain rice with nutritious rice germ.
Haiga is the word for rice germ in Japanese. Haiga rice is a fully milled kernel that retains its own rice germ. Haiga rice tastes and cooks similar to Japanese rice, yet preserves many of the kernel’s natural Vitamins and other nutrients.Tamaki Haiga rice is a very nice variety.
Before you prepare Japanese rice you have to wash it- be careful if you wash this kind, not to remove the rice germ.
This kind of rice tastes almost like white rice but is healthier. I like this kind very much.

Hatsuga Genmai

Hatsuga Genmai is a sprouted Genmai, brown rice.
You can do it by yourself: soak washed brown rice for 20 hours in warm water (38 °C or 100 °F) prior to cooking it. This process stimulates germination, which activates various enzymes in the rice. By this method, it is possible to obtain a more complete amino acid profile, including GABA. (Gammar Amino Butyric Acid)
Hatsuga Genmai it very nutritious, it contains fibres, magnesium, and Vitamin B1, B2, B6, and E.