@sheepdoge As I wrote earlier, it absolutely cannot be considered pedophilia, since pedophilia is the attraction to a person that have not reached the puberty stage. In other words, one whose reproductive system did not yet begin to function.
If someone can have a child of their own, they no longer count for 'pedophilia', regardless of their age. Even if they are 7 years old (there was a girl that age that gave birth). Karna is post-puberty, that's clear considering his reactions which do NOT appear until puberty and a surge of hormones that come with it.
As such, sex with Karna can, in no way, shape or form, regardless of the country in the world, be classified as pedophilia.
Depending on the country in the world, it can be classified as sex with a minor (which is NOT pedophilia, but a different crime altogether). But again, this varies from country to country and can be as low as 12 (9 for girls) years of age or as high as 21 years of age.
Since age of consent (the age from which a person can legally have give consent to have sex, thus their partner does not commit a crime by having sex with them) is a 100% cultural thing (unlike pedophilia which is 100% biological thing), it simply have zero relation to fiction. In fiction, age of consent can be 'since birth'. Though various countries still limit 'pedophilia' even in fiction, I don't think Japan is included in that list (yet, at any rate).