The relationship between Sehun and Kim ji hye could be perfectly described with one simple word,

'hatred' as they would say

'love' as others would say

Sehun and Kim ji hye has lived a majority of their lives despising each other, from preventing each other from getting anything they wanted to competing for anything and everything, they would stop at nothing to ruin each others lives. 

But how come they were the only ones that werent able to see the feelings that have been there all along?

Although they would forever deny they had something in common they did,

they were both complete idiots when it came to love.