Curry is Japanese comfort food. 9 out of 10, or almost all Japanese people would say that we grow up eating curry more than sushi or tempura. Some say it is our soul food, but all families have their recipe of curry, and mom's curry is always the best! As children, we eat curry once a week at school provided lunch.
Japanese curry was exported via England from India in the 18th century. That is why Japanese curry is more like stew, not like soup as in east Asian curry. In the 19th century, during the Russo-Japanese war, the first war, the people needed food that was nutritious yet easy to make in large batches. Curry over rice was the best match since we could stew anything inside, and seasoning with curry powder or mix would make it delicious. The army and marines both welcomed the food and the marines continued to eat curry every Friday on board. The veterans taught their wives when they returned home, and it helped their wives to not waste any ingredients and found it to be very versatile. The Navy self-defense forces still eat curry every Friday. Each ship has its own recipe, and there is an Annual Curry festival for civilians.
Later on, it became easy to make curry at home when manufactures invented a solid curry sauce. Then it became so easy to make Japanese curry, many families would cook it at home once a week, and children would even cook curry at summer camp by themselves. Now, you can find the ready-to-cook curry at any grocery store. Typically, Japanese curry is served over rice or udon, and in a soup regionally. Some people prefer next-day curry.