Which Japanese Shinkansen line was the first to open after the Tokaido Shinkansen?

The Sanyo Shinkansen was the first Japanese Shinkansen line to open after the Tokaido Shinkansen.

The Sanyo route extended high-speed rail westward from Shin-Osaka toward western Honshu and northern Kyushu. Its first section, from Shin-Osaka to Okayama, opened in 1972. The extension from Okayama to Hakata opened in 1975, creating a continuous high-speed corridor linking Tokyo, Osaka, and Fukuoka through connections with the Tokaido Shinkansen.

The Sanyo Shinkansen is sometimes confused with the Kyushu Shinkansen because services continue south of Hakata. The Sanyo line itself ends at Hakata Station, while the Kyushu Shinkansen continues into Kyushu. Trains such as Nozomi and Mizuho can cross the boundary between the Tokaido, Sanyo, and Kyushu systems, but the railway lines remain separately named.