I think tuna is one of the most popular items as a filling for many Japanese, that goes well with both rice and bread.

Also the combination of tuna and mayonnaise is very popular in Japan.

Amazon.com: Online Shopping for Electronics, Apparel, Computers, Books, DVDs & more

Taste
★★★☆☆
Good. Familiar taste for Japanese!
Price
★★★☆☆
Around 110 yen per package.
Calorie
★★☆☆☆
289 kcal per package.
Easy to get?
★★☆☆
I got this at Seven-Eleven, one of the biggest convenience stores in Japan.
I’m not sure if we can get it anytime.
Get again?
★★★☆☆
Not sure for now.

The ratings above are completely my personal comments, see here for the details.

The materials may be changed in the future so please check yourself when you try it.

Open the package. View from above.

View from a bit side.

Cut in half.

2020 Mar.

Amazon.com: Online Shopping for Electronics, Apparel, Computers, Books, DVDs & more