What is the bright red ingredient in Japanese chicken curry katsu?
This appears to be a Japanese pickle mixture, made with daikon radish amount other things, called Furkujinzuke. 


  Fukujinzuke is a mixture of Japanese radish (daikon), lotus root, cucumber and eggplant which are preserved in a soya sauce and sweet cooking wine (mirin) base. The sweet brown or red relish is served as a garnish to Japanese curry (kare raisu).


Source: https://www.japan-guide.com/e/e2349.html