エッチなお姉ちゃんが、褐色巨乳の悪魔だった件

When he wakes up one morning, the protagonist who is an only child, finds himself having an older sister―― She has tanned skin and a voluptuous body. While being confused, she takes his underwear off as a matter of course, and gives him a blowjob.

My brother's sperms belong to his sister...... Having said that, she starts sucking his cock.

Is this a dream, or is this some kind of delusion――

But in reality, his self-proclaimed sister―― Is a demon who has been summoned to this world accidentally～a succubus.