Death Game Manga no Kuromaku Satsujinki no Imouto ni Tensei shite Shippai shita (2021)

Death Game Manga no Kuromaku Satsujinki no Imouto ni Tensei shite Shippai shita

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.

(Source: Kadokawa, translated)