They Say That If You Defeat the Devil, You Can Go Home

In the fifth year after being summoned to another world, I defeated the Demon King. Amid the cheers, I waited happily to go home. But the world froze. The sky cracked. A voice told me: "Thank you, ninth key. Program, start resetting." I'm the ninth. The first eight stayed behind that door forever. This time, it's my turn. ——But I had no intention of going in.