I Killed the Demon King. It Was a Mistake

[Congratulations on seeing all the endings of the Valent Saga.] [From now on, you can select the hidden origin ‘Demon Race’.] I was born as a Demon after falling into the game world and a whole 3 years have passed. The nameless Allied Forces soldier, Mil of the Sky Knight Order, Barbarian Knight Barre. And the doppelganger and spy of the Demon King’s army, Seo-han, are all me. But I… “Y- you, what the heck… Bam!” I ended up blowing off the Demon King’s head. Huh? This isn’t right.