"There's a very thin line between LOVE and HATE". Maybe just because you hate or hurt that person is in fact you love him/her. Izaya never knew that quotation so as Shizuo but what happens if they both feel it? At first, things gone smoothly. But there's no such thing that is forever perfect...
They never knew that loving a person is much harder than hating them.
Disclaimer: Any recognizable characters are not mine and do belong to their respective owners. The only thing that's mine is the plot and some own characters.