My Big Sister Lives in a Fantasy World

One day out of nowhere, high schooler Yuichi Sakaki begins seeing words above people's heads. It turns out to be the ability to see people's true natures, which he names... Soul Reader!

(Actually, his big sister names it that.)

The next thing he knows, he's surrounded by people with bizarre labels like "Zombie" "Vampire" and "Witch." And before he can figure out what to do about that, he finds himself threatened by a beautiful girl, Natsuki, whose label is "Serial Killer"!

Fortunately, Yuichi is not unprepared. His big sister has been training him for this kind of thing all his life. The battle is about to unfold between the bloodthirsty killing machine... and the world's strongest little brother!

(Source: J-Novel Club)