Sinillyuui Sarang

The main girl's older twin brother is an enhanced human. People like him are genetically engineered as a human survival project. She is constantly being compared to him and is always trying her best to catch up to her twin.
She meets another enhanced human, Iron. They fell in love with each other.
But there are many obstacles: an accident making her to live her brother twin's life. Such as the conspiracy to create a super human commanding all enhanced humans. And the candidate is Iron. Such as Iron is unconsciously turning into a beasty killing machine.