Roll.EXE is a NetNavi (short for internet navigator) operated by Maylu Sakurai. She is also Maylu's elder sister Kara Sakurai, having been ressurrected after her death as part of SciLab's Human Navi Project.
Initially created from Yuriko Ozono's DNA as part of Project: ELYSIUM, Kara lived with her younger sister Maylu in a house in the countryside 5 Kilometrers from DenTech City. Due to the nature of cloning technology she and Maylu both inherited the abilties and key memories of their mother. In addition both clones gained healing powers granted to them by Slur.EXE, who saw them as her sisters.
Death and Ressurrection
Shortly after Maylu was kidnapped by a black maket slave trading ring, Kara began to develop heart complications and died. Following her death however, Yuriko combined her genetic material with NetNavi programming, giving her new life as a NetNavi, Roll.EXE.