I don't know what you should do first. Any option you choose will spoil you for the other party. If you read fanfics first, you'll think the anime is going to be awesome and have a rich plot and will be sadly disappointed. If you watch the anime first, maybe you won't love Schwarz (the bad guys) as much as you should because they're a bit underdeveloped and plain. It's a tough decision.
I think that, everything you need to know is that the series is about a group of four (utterly gay) men who are florist at day and assassins at night (the premise is just too good to be true), cleaning Tokyo from the evil doers Justice can't reach. Of course, they all angst about their moral dilemma (I'm a killer, I don't deserve happiness, yadda, yadda...) AND about their tragic pasts. Later on, you're introduced to their nemesis (they're Weiß=White, the other team is called Schwarz=Black), who are awesome and possess psychic superpowers. There's a try of general plot between the organization that controls Weiß, the organization that controls Schwarz, Schwarz's plans aside their organization, Weiß' individual conflicts and all the secondary characters bound to die in the process.
See? Now you know all you need to dive into the world of WK fanfiction. Careful with the Mary-Sues and exalted Aya (Weiß' main character) fangirlism, though.
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I think that, everything you need to know is that the series is about a group of four (utterly gay) men who are florist at day and assassins at night (the premise is just too good to be true), cleaning Tokyo from the evil doers Justice can't reach. Of course, they all angst about their moral dilemma (I'm a killer, I don't deserve happiness, yadda, yadda...) AND about their tragic pasts. Later on, you're introduced to their nemesis (they're Weiß=White, the other team is called Schwarz=Black), who are awesome and possess psychic superpowers. There's a try of general plot between the organization that controls Weiß, the organization that controls Schwarz, Schwarz's plans aside their organization, Weiß' individual conflicts and all the secondary characters bound to die in the process.
See? Now you know all you need to dive into the world of WK fanfiction. Careful with the Mary-Sues and exalted Aya (Weiß' main character) fangirlism, though.