You wake up one morning with a headache, you wonder if you're hung-over but you didn't drink anything last night so that can't be it and after taking a painkiller and heading to work you forget all about it. A few days later you think you back to your childhood and there's a memory that doesn't fit, it doesn't make sense and you try not to think about it because it sets you on edge and makes you feel uncomfortable.
It doesn't stop.
Maybe weeks go by, or maybe it's months, and someone turns up on your doorstep. Maybe they look official, or maybe they're wearing jeans and a T-Shirt, but they introduce themselves and tell you that they're from something called 'The Agency', they sit you down and if you're lucky they'll make you a cup of tea or pour you a drink before explaining it all to you.
The memories are real, but they're someone else's, someone you always thought of as fictional. You're what they call a reincarnate, someone who's been reincarnated from this fictional person, brought into this world with magic that no one yet understands.
They talk about a war that's being fought between two sides of reincarnates, the good and the bad. You're not told what side to pick or that you need to, but you know that a day will come when you and the person you used to be and are possibly becoming will need to choose.