I Reincarnated as the Little Sister of a Death Game Manga's Murd3r Mastermind and Failed is a Manga/Manhwa/Manhua in english language, Horror series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.nl fastest updating comic site. The Summary is

One day, Mai remembers that her perfect stepbrother is a character in a death game manga, and that one year later he will hold a death game involving all of his classmates, killing his sister in the process. Mai plans a variety of surprises for her stepbrother every day based on what he said in the manga, "Nothing unexpected happened, so I was bored," but as the days go by, he begins to show abnormal signs...

Only I know what my brother's really like. Pepu's comicalization of Inada Sou's popular web novel!