do kills in annex count towards the "seriously" achievement?

No they don't, or at least I'm pretty sure they dont. I've been told the only kills that count are in the other game modes, such as warzone, execution, and assasination. By the way. When you get 10,000 kills, you may not get the achievement, there are a lot of contribuiting factors to the achievment. Say if you got 10 kills, but quit from the game mode early, based on how early you quit, some or all of your kills wont be counted. And also sometimes kills are "glitched" not meaning you glitched to get them, but for some reason, they werent counted, that could be caused by either something as simple as a moment of lag, or a bug that didnt count them. Some people have gotten as many as 15,000 kills before getting the achievment, so don't be surprised if you get 10,000 kills, but no achievment. Also if when you do get the achivment, you unlock a special gamer picture