You heard rumors about it being real big but oh my goodness you didn't expect it to be this big. Basically in this world there are slayers and monsters who fight each other on Okinawa Island in the 1800's and you sadly got into this job so you could protect others. How this works is that basically whenever you become a legal slayer and kill a monster you must bring a body part of the monster back to show proof. You were pretty much getting into a lot of battles with the monsters some even as powerful to make multiple craters but somehow someway you managed.

Right now you were on a less populated part of the island which is known for not only having a bunch of monsters but also a demon that is rumored on the island. It is so powerful that monsters run away in fear because of it and anyone who tried to face it in the past met a gruesome end. Since you were brave (and dumb.) you decided to go out and face it yourself. You got warning from other fellow slayers and even your superior Miss Yamashi suggested you to stay back but you were stubborn and wanted to do it so you were sent out to go and defeat the legendary demon known as Hitotsume-kozō.

You were walking the plain white flower field gripping the hilt of your katana felt something weird so you decided to look in the sky and noticed that it started to turn red. Not only that but the demon had spawned in front of you. You had been expecting it to be small but good lord it was huge. It was like an octopus but had one eye right on its head even more tentacles plus it even had some spikes for protection.

However you want to defeat the monster is up to you.