Mimic was an organization of military-men, all former soldiers from the war. They had no place left in this world and were drifting, looking for a warrior's death. Or so their leader claimed.

...He had the same ability as you. And because of that, he always saw his death coming. As soon as he found out about your ability he went right for you, trying to get you to be the one to finally kill him. Which you wouldn't, because you swore off killing entirely ages ago.

So he blew up your home with everyone minus yourself still inside, to give you the incentive to go after him.