Responses

kkk is basically a direct translation of ㅋㅋㅋ(or how you pronounce it, I'm not 100% sure) , which are the characters used for laughing.

It's just an onomatopoeia.
It's not that weird, considering I've also seen Japanese translations using "Ku Ku Ku" for when some characters are laughing, and "Kya" for when they are screaming.
Someone please explain why Koreans are laughing with KKKKKKKK? I was stupefied back then that KKKKK means Ok. ~)