I assume katsu curry is the biggest invention of gastronomy in Japan. The person who invented this dish should be genious. It is told that a famous Japanese baseball player asked the cook to put his two favorite dishes, tonkatsu and curry together. Not like, sandwich, katsu curry was not invented due to play card games during the meal but to enjoy two dishes during one meal.
Actually both dishes are not originally from Japan. Tonkatsu, usually shorten to katsu is a fried pork cutlet, European pork schnitzel adapted to Japanese style using panko breadcrumbs. Curry is originally from India but Japanese version was introduced via UK. Curry itself is less spicy but smoother than the Indian style.
This is the one of the dishes you must try in Japan!