Tokaido Shinkansen is the oldest and busiest Shinkasen line and it is operated between Tokyo, Nagoya, Kyoto and Osaka. Sanyo Shinkansen is operated between Osaka, Okayama, Hiroshima and Hakata (Fukuoka). Both lines are connected each other. Many trains, “Nozomi” that is the fastest train on Tokaido-Sanyo Shinkansen, run from Tokyo to Hiroshima and some of those run to even Hakata.
Most of Hikari run between Tokyo and Shin-Osaka, But some of those run to Okayama and Hiroshima.
Sanyo Shinkansen connected to Kyushu Shinkansen at Hakata. Many trains, Mizuho and Sakura are operated between Shin-Osaka and KUmamoto or Kagoshima-Chuo directly. Please see the post, Kyushu Shinkansen to get details.
I have received the email from JR West. They confirmed Japan Rail Pass can be used for Kyushu Shinkansen. But Japan Rail Pass can be used for only Sakura that is the second fastest train between Shin-Osaka and Kagoshima-Chuo. We cannot take Mizuho that is the fastest train between Shin-Osaka and Kagoshima-Chuo by Japan Rail Pass. JR West and Kyushu applied same fare table as Nozomi. So Japan Rail Pass does not cover even the basic fare. If you take Mizuho, you have to pay the full fare.