[Demon Slayer] The Demon Eater

This story is also known as "[Demon Slayer] The Color Out of Space."

Here's the blurb:

Ibuki is a pitiful kid whose parents are dead. He doesn't have a little sister, but he does have a house.

He makes a living selling flowers. His yard is a garden, and there's a well beside it. Though you can't exactly call him a flower seller, since his garden is also full of medicinal herbs.

Ibuki: I may not have a little sister, but I do have an older sister!

Demon: This guy looks delicious!

(They gobble the demons up in one bite.)

The scumbag boss, realizing that demons are dying for no apparent reason: ???

Much later

Ibuki: Are you the ones who hurt my sister?

Douma: Oh, what beautiful eyes you have! I've never seen a color like that before! Become the next Holy Son of the Paradise Faith!

Muzan: Don't come near me! Aaaaaah! Aaaah!

In the past, there were demon slayers. Now, there are demon eaters.

Here's the serious blurb:

Someone once said Ibuki's green eyes were as beautiful as a forest.

"But... behind the forest lies a color from the stars."

"It's the most dangerous thing there is."

The black-haired, green-eyed boy clearly disagreed.

Theme: "It's a color from the stars."