Refund for canceling train tickets?

Hi,

1) Will I be offered a full refund (basic fare + limited express fee) if I were to cancel a train ride eg. Sunrise Seto at a "Midori no madoguchi" counter?

2) If I were to book tickets as above prior to activating my JR pass, will I also be eligible for a refund when I activate it?

Hello.

You can get the refund by deducting 220yen on basic fare.

And you can also get that refund by deducting 330yen on limited express fare if you cancel the ticket by two days before.

If you cancel after one day before boarding,you need to be deducted 30 % of limited express fare.

https://www.jreast.co.jp/e/ticket/changes.html

Thank you!

You don't need to pay for the tickets if you'll be using a JR Pass. Exchange the voucher and let them know which date you wish to activate the pass and then reserve the tickets. You can reserve tickets with a pass that is not yet active provided it will be active on the date you're reserving the ticket(s).