Is Rogue a sequel to Black Flag? (present)
Hi. So, although I am a huge fan of the Assassin's Creed series, the last game I bought from the series was AC III. And it's not because I don't want to buy, or I'm getting bored of the series (I think I'll enjoy every AC, just not as much as others) but I had kind of a problem to buy the games. But now, I want to buy the games that I miss. And because I'm waiting to buy my PS4 to buy AC 4 Black Flag and unity, I thought about buying Rogue for my PS3. So I wanted to ask, is Rogue a direct sequel to Black Flag? Is the story in the present connects to the one in Black flag? Do I have to play Black Flag before Rogue? Thanks for answering. 
In terms of the historical narrative AC Rogue is more of a prequel to AC3 than it is the sequel to Black Flag. I don't think you'll have any problems understanding the story or spoiling parts of Black Flag if you play Rogue beforehand.
In terms of the Modern day narrative it is kind of a sequel though. Black Flag and Rogue have a similar modern day story set-up and Rogue's story happens shortly after the events of Black Flag's modern day. If you don't want to spoil yourself on the "events" of Black Flag's modern day you could avoid reading the e-mails and listening to the sound clips that can be found because I don't think the main story mentions the events of Black Flag explicitly.
Hope this answers your question.
It's a sequel to Black Flag and prequel to AC3. The modern day is about the same as Black Flag's sections. It references a few things from that game and the ending to AC3. I don't think you'll need to play Black Flag to catch yourself up before playing Rogue. To me, story-wise, it serves as a better prequel to AC3 than anything else. You see things building towards Connor's time more than results from Black Flag.
Yes. It's a sequel to black flag, both in modern day and in the past,... but moreso in the modern day. a lot of the people you see in rogue are from both black flag and AC3. you, as the player, should feel an attachment to/know the history of a specific character from black flag/freedom cry, for example.
“Force has no place where there is need of skill." Herodotus
I know that Shay's story line is like a prequel to AC3, I was talking about modern day. But your answers overall helped me. Thanks.