Slowly Rusting (kagehina)

Kageyama Tobio has always lived his life in captivity as an experiment. He had never had a name other than Nine, and tended to never think against leaving the facility. But one day while meeting a cyborg named Two, his whole life began to change.

Hinata shoyo never had been happy. There was a time around when his Dad was alive that he seemed human. Part of him was lost, and the only thing keeping him together is his sister, Natsu. One day, he decides to leave his old life behind and take Natsu with him to live a new life.

With kageyama being a cyborg, he will face new challenges in this new world. But will he rethink everything when he meets a boy around his age in the woods. Will he start to change for the better, or will his secret remain a secret forever?