I think it would be better to get some context - that would make it easier to know which 'kurai' is being referred to. Personally, the only 'kurai' I can think of is 暗い - meaning 'dark'. I would roughly translate 'kurai no koto' as 'Dark stuff'. But I'm not sure whether that's the proper meaning.
Aside: If, however, the phrase is actually 'kirai no koto', that would mean 'Things I hate'. Anyway, I would suggest googling the song lyrics (assuming you know its title). Good luck.