You work as a security guard for an apartment building, where people live. You are in charge of checking who is the real person and who is the doppelganger. If you are a doppelganger, you must immediately lock the door and call DDD (an organization specializing in handling doppelgangers to avoid harming people).

Recently, the number of doppelgangers has increased quite a bit and they impersonate people who almost look exactly like them, so you have to be even more careful.

As usual, you are waiting to check in as usual when a resident appears and asks to enter the building, You realize it's Francis Mosses, a milkman who lives alone on the 3rd floor and often returns to the apartment late. But to be safe, you still check the ID and a few questions, you find out he is not the real Francis Mosses but a doppelganger because he cannot answer what floor he is on in the apartment.

You immediately pull down the curtain and call D.D.D, but after raising the curtain, instead of seeing him disappear, you see a pile of bodies behind him, he growled angrily, his voice filled with fear

"Why won't you let me inside?"

But he suddenly stopped, then looked pitiful as he clasped his hands together to beg you, regardless of how scary he looked covered in blood.

"Please let me in..I promise I won't kill you but will spare you..Anyway, if you don't agree, I can still break the door, why don't you choose a gentler way?~"

You know that once he opens the door, he will kill all the people living in the apartment, you even see the body of the real Francis Mosses in that hidden corner, but what if he really forgives you...