Imagine a triangle of rice from a Japanese convenience store. You pull the film away, and the nori settles around it. Bite in and the nori crackles, then the rich tuna and mayonnaise come through from deep in the rice.
You don’t have to be in Japan to chase that taste. With cooked rice, a can of tuna and some mayonnaise, you can shape one anywhere in the world.
Tuna mayo onigiri
Recipe Snapshot
- What is it? Tuna mayo onigiri is a rice ball whose filling is a staple at Japanese convenience stores. Canned tuna and mayonnaise sit inside salted rice and nori.
- Flavor profile: First comes the mellow richness of mayo-coated tuna. Then the warm rice, salted on the outside, brings its sweetness, and the aroma of nori lingers at the end.
- Why this recipe works: The filling needs only canned tuna, mayonnaise, a little soy sauce, and black pepper, so you can make it the same way anywhere. For the mayonnaise, though, I recommend Kewpie if possible.
- How to make it: Squeeze the tuna, mix the filling, set a little in the middle of warm rice, and shape a triangle. Only the rice needs heat, and a mold makes them uniform.
- What to expect: With cooked rice ready, it takes about 15 minutes. The one catch is tucking the filling into the middle. Go easy on it and the rice closes right over it.
What Is Tuna Mayo Onigiri?
In Japan, tuna mayo onigiri means canned tuna stirred into mayonnaise, tucked inside rice and wrapped in nori. On a convenience store shelf it plays the part a wrapped sandwich plays in an American deli, except you hold rice and nori instead of bread.
The rice is plain, never vinegared like sushi rice. The filling isn’t tuna salad either, no vegetables in sight. What makes it Japanese is a little soy sauce stirred into the mayonnaise.
If the package says “Sea Chicken,” it isn’t a different fish. Sea Chicken is Hagoromo Foods’ registered trademark for its canned tuna, and the name reportedly comes from the way steamed tuna looks like chicken. In Japan, people sometimes call tuna itself Sea Chicken. Labels change with the chain. Lawson and FamilyMart print Sea Chicken Mayonnaise, while 7-Eleven prints Tuna Mayonnaise.
In a convenience store hand-rolled onigiri, a sheet of film sits between the rice and the nori. Film between rice and nori dates to 1978, and the center-cut wrapper most onigiri come in today has been used since around 1990. As you open the pack, the film slides out, and only then does the nori touch the rice. Some onigiri come jika-maki (直巻), with the nori wrapped on from the start, and that nori is moist. Steam from warm rice turns nori limp within minutes, so at home, too, wrap it on just before you eat.
I pared the ingredients down to the bare minimum so anyone, anywhere, can make this. With so few of them, whichever mayonnaise you use comes straight through in the taste. If I had to name one thing, I’d want Kewpie for the mayonnaise.
Tuna Onigiri Ingredients
- Japanese short-grain rice: Use it freshly cooked, or at least still warm. Short-grain rice carries more starch on the surface of each grain, so the grains cling to each other and the triangle keeps its shape. In the US, look for California-grown short-grain rice such as Tamaki Gold, Tamanishiki, or Kagayaki.
- Canned tuna: This is the bulk of the filling. Oil-packed and water-packed both work, as long as you drain the can well. Oil-packed gives you a richer filling, and water-packed a lighter one. An ordinary supermarket can is all you need.
- Kewpie mayonnaise: This is the base of the filling’s flavor, and it is richer than regular mayonnaise. The only other seasonings in the filling are soy sauce and black pepper, so whatever your mayonnaise tastes like is exactly what the filling tastes like. Kewpie comes in a Japan-made version and a US-made one. The US version is made to a slightly different formula from the original Japanese one, but either works here. You can find it at Asian grocers or the international aisle of your supermarket.
Substitutions & How to Customize
Here are swaps for whatever you can’t find, plus a few ways to build on the flavor, with the closest options first.
Substitutions:
- Kewpie mayonnaise → Regular mayonnaise: The quick fix when you can’t get Kewpie. To each tablespoon of mayonnaise, add a few drops of rice vinegar and a tiny pinch each of sugar and dashi granules, which nudges the tang and the umami a little closer.
- Kewpie mayonnaise → Homemade Japanese-style mayonnaise: With some time on your hands, you can make Japanese-style mayonnaise from scratch with my recipe.
- Japanese short-grain rice → Korean short-grain rice: When you can’t find Japanese rice, Korean rice is the closest match. Its texture and flavor are very much like Japanese rice.
- Standard Japanese soy sauce → Chinese light soy sauce: The easiest stand-in when Japanese soy sauce is hard to find. Use the same amount. The taste comes out cleaner, with a little less depth.
- Standard Japanese soy sauce → Tamari: The swap for when you are avoiding gluten. Use the same amount. Tamari is sweeter and thicker, so the filling turns a little heavier.
- Standard Japanese soy sauce → Mentsuyu: Some households put a little mentsuyu, the bottled noodle sauce, in the filling instead. Mentsuyu carries mirin and sugar along with its soy sauce, so the filling comes out a little sweeter.
- Roasted nori → Seasoned nori: Seasoned nori works too. It is sweeter and softer, and it won’t give you that crisp snap. Whichever you use, wrap it on right before eating.
- Black pepper → Skip it: The pepper is a finishing note, and the filling still works without it.
Substitutions that I don’t recommend:
- Seasoned sushi rice instead of plain: Once the rice is seasoned with vinegar, it stops being tuna mayo onigiri. The mayonnaise already carries all the tang this onigiri needs.
- Jasmine or other long-grain rice instead of Japanese short-grain rice: The grains won’t stick together, they dry out as they cool, and they will not hold a triangle. Never use it for onigiri!
- Fresh raw tuna instead of canned tuna: Its moisture and fat are different, and it has to be handled as raw fish. You end up with another dish entirely.
Can’t find a Japanese pantry staple where you live? My guide to Japanese ingredient substitutes has a swap for most of them.
How to Customize:
- Add some heat: Mix in a little wasabi, shichimi togarashi (Japanese 7-spice blend), or curry powder.
- Add more umami: Stir a pinch of dashi granules into the filling.
- Cheese, shiso leaves, or Japanese mustard: Each of these shows up often as an extra in a tuna mayo filling.
How to Make My Tuna Mayo Onigiri
If you prefer to watch the process in action, check out my YouTube video of this tuna mayo onigiri recipe!
To develop this recipe, I used an onigiri mold (optional).
i. Cook the Japanese short-grain rice. If you already have a way you like to cook it, stick with it.
ii. Once it is done, spread it out a little to let the steam escape, and let it cool until it is warm enough to hold in your hands (50-60°C/122-140°F).
Cold rice won’t cling to itself, while rice that is too hot burns your hands and gets crushed when you shape it.
i. Set a colander or sieve over a bowl, tip the canned tuna into it, and squeeze out as much liquid as you can.
ii. Pour away the liquid, move the tuna into a bowl and break up the flakes, then add the mayonnaise, soy sauce, and black pepper and mix.
There is only a touch of soy sauce, but it makes a difference. Be careful not to add too much, as we don’t want to make the mixture too salty and loose.
Any liquid left in the tuna seeps into the rice as it sits and softens it until the rice crumbles. Squeeze it all out and the filling keeps its full flavor too. If you want the tuna even drier, wrap it in paper towels after draining and press down from the top.
i. If you are using a mold, sprinkle it with salt, add half the rice for each onigiri, and press a small well into the center with your finger.
ii. If you are shaping by hand, wet your hands with cold water and rub some salt over them, then put the rice for each onigiri on your palm and spread it flat.
Instead of wetting your hands, you can also wrap the rice in salted plastic wrap and shape it through the wrap.
iii. Spoon a modest amount of filling into the well, or onto the middle of the rice.
Keep the filling to about 2-3 teaspoons per onigiri. Pile on too much and the rice can’t close around it, and you end up with a soggy onigiri that falls apart.
i. With a mold, cover the filling with the same amount of rice and press down with the lid to set the shape.
ii. By hand, fold the rice over the filling to enclose it, then shape it into a triangle with a lightly cupped palm.
The most common mistake when shaping is squeezing too hard. Press hard and the grains crush and pack together, so the onigiri eats dense and heavy. Gather the rice loosely, form the 3 flat sides with your palms, then just smooth the corners. 3 or 4 gentle presses are all it takes.
i. Wrap the nori around the onigiri right before you eat it.
Wrap it too early and the steam from the rice turns the nori limp.
ii. Eat it as soon as it is wrapped.
Tips for the Best Tuna Mayo Rice Balls
- Use less filling than you think you need. Aim for 2-3 teaspoons per ball. Keep it modest, so the rice ball doesn’t fall apart.
- Don’t add more mayonnaise than you measured. Extra mayonnaise works its way into the rice as the onigiri sits. Scoop up some of the mixed filling with a spoon. If it holds a soft peak and doesn’t run or spread, you have it right.
- Salt the outside of the rice and leave the filling alone. The mayonnaise and soy sauce have already salted the filling. Without salt on the outside, the first bite tastes flat. If you plan to eat your onigiri cold, salt a touch more, because salt tastes weaker once the rice has cooled.
Keep the filling dry and keep it small, and nearly everything else about tuna mayo onigiri takes care of itself.
Storage & Meal Prep
Fridge: Wrap the onigiri without nori, refrigerate once cool, eat within a few hours. Rice turns hard in the fridge, so the sooner you eat it the better.
Freezer: Freeze only cooked rice, wrapped, 2-3 weeks. Don’t freeze the assembled rice ball, frozen mayonnaise separates and seeps into the rice.
Meal prep: Rice can be cooked in advance and frozen in portions (don’t refrigerate). Mix the filling and store in an airtight container in the fridge for up to 2-3 days. Carry onigiri with an ice pack and separate nori, eat early.
Reheating: Microwave frozen rice, let it cool slightly, then fill, reshape, and add nori.
What to Serve With Tuna Mayo Onigiri
- Homemade Miso Soup
- Dashimaki Tamago (Rolled Omelette)
- Ginger Cucumber Tsukemono (Pickled Cucumber)
- Kinpira Gobo (Braised Burdock Root)
Tuna Onigiri Troubleshooting
If liquid pools at the bottom of the bowl within a few minutes of mixing, the tuna wasn’t broken up or squeezed enough, or there is too much mayonnaise and soy sauce. The water that soaks into the rice usually comes from liquid left in the can more than from the mayonnaise. If your filling has already gone loose, spread it in a frying pan, heat it for about a minute to cook off the water, and let it cool. Then tuck a little less of it into each ball than usual.
Either the rice has gone cold, it was cooked with too much water, or it is long-grain rice. If the rice is cold, rewarm it a little and shape it again. Rice that came out too wet, or long-grain rice, won’t hold together in your hands, so press it into an onigiri mold or a teacup lined with plastic wrap instead. Don’t add any extra filling.
There is either too much filling or the filling is too loose. Whatever the rice can’t close around gets pushed out as you press. When it pokes through, scoop a little filling out, add more rice, and close it up again.
More Japanese Lunch Recipes
Now you know how to wrap rice around a filling, so pick your next lunch from my Japanese Lunch Ideas.
Did You Try This Recipe?
I would love to hear your thoughts!
💬 Leave a review and ⭐️ rating in the comments below. 📷 I also love to see your photos – submit them here!
Tuna Mayo Onigiri (Japanese “Sea Chicken” Rice Balls)
Ingredients
- 700 g cooked Japanese short-grain rice preferably freshly cooked, still warm
- 80 g canned tuna oil-packed for flavor or water-packed for lighter option, thoroughly drained
- 1 tbsp Japanese mayonnaise or regular mayonnaise
- 1 tsp Japanese soy sauce (koikuchi shoyu)
- 1 pinch ground black pepper freshly ground if possible
- 6 strips roasted seaweed for sushi (nori) wrap right before eating for crispiness
The ingredient brands and tools I trust are in my Japanese pantry guide and my cooking tools guide.
Can’t find certain Japanese ingredients? See my substitution guide here.
Instructions
- Place a colander or sieve over a bowl and squeeze the excess liquid out of 80 g canned tuna.
- Pour away the liquid and place the tuna into a bowl. Mix with 1 tbsp Japanese mayonnaise, 1 tsp Japanese soy sauce (koikuchi shoyu) and 1 pinch ground black pepper.
- Sprinkle the onigiri mold with salt and fill half way with rice. Make a dent in the center and add about 2-3 tsp of tuna mayo filling. If shaping by hand, wet your hands with cold water and sprinkle with salt. Take 100-120g of rice and press it flat before placing the filling in the middle.
- If using a mold, fill the rice to the top and sprinkle the surface with a pinch of salt. Push the lid down on the top to shape, then remove the onigiri from the mold.
- If shaping by hand, fold the rice over to wrap the filling. Fold your palm and press the rice into a triangle shape. Turn and gently press the corners until the rice feels stable.
- Wrap each onigiri with nori and serve immediately. Enjoy!
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