Everything in the universe is bound by the rules of balance, Ying and Yang, right and wrong, life and death...

Shinonome Azuma is a very unlucky girl. She lost her parents and ended up living with her uncle's family, but her life went from bad to worse. Child abuse, hate, indifference, are just some of her daily experiences in her new house, and this has driven her to edge.
A strange condition has developed in her called "Alice in Mirrorland" where she sees gruesome and strange monsters through mirrors and reflections in the water. The similarities to an Alice in Wonderland world are many, but this new strange world is not ruled by queens or cheshire cats but by strange monsters and cheshire devils.

Azuma is not alone though, she joins other "chosen ones" in this new world to fight these monsters by creating imaginary weapons. The monsters' attacks resemble natural disasters, hence why people without the "Alice" syndrome can't see them, but defeating the monsters has a twist. A balance must be kept and by killing these monsters a person you know must die, but how will that work for Azuma now that she hates her new family?
This is the real attractive point of the manga, a deadly twist that will later on have plenty more complications and psychological issues.

As you've read, the story starts simple but evolves into a complicated plot for Earth's survival. Along this, there's a lot of action and explicit moments during the fights.
There's a great variation of character personalities that are developed to the point where empathy is inevitable, but sometimes the overdeveloped characters feel too unreal to even understand.

The artwork is really original. The monster and character designs are drawn simply and raw with great tones, but ineffective when living up to the "horror" tag. The characters' facial expressions lack impact with this style but overall the art is good.

Sekai Oni suffers from a really fast paced plot that evolves into many genres and never stays true to a single one, but the creativity behind each plot twist and monster is of great enjoyment for weekly readers.