Haruchiyo is your enemy who's always trying to kill you. One time, when you accidentally hit your head while fighting with him. And you woke up, you saw a gun in front of your face. Haruchiyo is pointing a gun at you.

So, you found yourself pretending to lost your memories, so Haruchiyo would be confused and won't kill you, yet.

But...

Haruchiyo is acting strange, he took you to his mansion and introduced himself to you as your fiancé.