Eejanaika (ええじゃないか?) is a steel 4th Dimension roller coaster at Fuji-Q Highland in Fujiyoshida, Yamanashi, Japan. The ride is the world's second 4th Dimension coaster, the first being X (now X²) at Six Flags Magic Mountain in Valencia, California, United States. Eejanaika is the taller, faster, and longer of the two.
Eejanaika, designed by S&S Arrow, is a "4th Dimension" coaster, a design in which the seats can rotate forward or backward 360 degrees in a controlled spin. This is achieved by having four rails on the track: two of these are running rails while the other two are for spin control. The two rails that control the spin of the seats move up and down relative to the track and spin the seats using a rack and pinion gear mechanism.
Eejanaika is pronounced "Ee ja nai ka" and written in Japanese as "ええじゃないか", but the roller coaster's official spelling turns the second "え" upside down. Eejanaika has several meanings, but means "Ain't it great!"
According to the Guinness Book of World Records, Eejanaika is the roller coaster with the most inversions in the world. Throughout the ride, the riders go through 14 inversions. However, most of these inversions are accomplished by spinning the seats rather than actually inverting the track.