Maguro-don is one of my favorite Japanese recipes. It's very healthy and you can make it with reasonable ingredients from grocery stores in Japan. Perillaseed oil has a lot of α-Linolenic acid(Omega-3 fatty acid) and tuna(blue skin fish) has omega--3 fatty acid, EPA and DHA which are known to reduce the risk of heart diseases and have other benefits.
Maguro-don is a traditional Japanese dish, but recently tuna is becoming endangered due to overfishing. Because Japanese people eat so much tuna we have started investing in tuna farms to grow tuna in captivity so we can save the wild population. Unfortunately many people still prefer wild tuna and it can be difficult to find farmed tuna to buy. In place of tuna in this recipe you can also substitute salmon, squid, shrimp, buri, or katsuo tuna, which is not endangered.