If you are visiting Japan, you may have a chance to take Hello Kitty themed Shinkansen or Bullet Train. The Hello Kitty Shinkansen is running for a limited time until November 2018.
Please check the Japan Rail Pass Blog and you can find the detailed information on what the Hello Kitty Shinkansen is all about.
The Shinkansen is served by Sanyo Shinkansen (the West region of JR service from Osaka to Fukuoka)
The best part is, you can use the JR Pass.
To make sure your train is Hello Kitty themed, I recommend you to reserve your seat. If I were you, I would go to the ticket reservation booth, called MIDORI NO MADOGUCHI, and speak with the officer working there.
Enjoy your shinkansen trip with Hello Kitty!