"Onii-tama?"
Cain, who reincarnated as one of the love interests of an otome game, screamed at the loveliness of his sister, Diana. I can't believe that this angel is going to be a villainess with countless bad ends-- No, there is no way that such a future can exist!
Clenching his fist tightly, he raises his sister into a gentle lady, while also dispelling the darkness held by the love interests in place of the heroine.
Relying on his game knowledge from his previous life and an orphaned chamberlain. Everything for his beloved sister-- The brother's challenge begins now!