S1·E18 The Evil Shadow Soldiers

he operator, Kei Yuki, goes to visit her parents' grave. There, her father's ex-pupil, Kazuya, shows up. They had attempted to make a space colony not out of machines, but with nature exactly akin to Earth's. However, the experiment failed and Kazuya, the lone survivor, returned to blame her father who had lost his life there. But now he regrets this and wants to continue the research