Arun was scientist on Kirith who had assisted the Panjistri in breeding the Homunculus. When she began investigating their reasons for doing so, they subjected her to genetic experiments which badly mutilated her. She escaped to the Darkfell, along with other Kirithons who had undergone similar experiences and called themselves the Unlike, with Arun as their leader.
After Ace fled from the Panjistri laboratory where the Homunculus was kept to the Darkfell, she met Arun, who told her about herself and the Panjistri. Afterwards, she agreed to help Ace if she would get the Seventh Doctor to help heal her people and the Darkfell. She and Kraz accompanied Ace back to the Harbours in time to see Raphael free himself and Miríl. While there she tried to kill the Homunculus but was stopped by Raphael, who argued for saving it instead but was forced to kill it himself.
After helping to convince Tanyel of the truth, Arun accompanied Ace and Raphael to Kandasi Island, where they met with the Doctor and teleported themselves to the real Kandasi, where they learned from Reptu of the Panjistri's plan to create the God Machine. When the station's systems began failing, Arun and Reptu evacuated the other Panjistri to Kirith. (PROSE: Timewyrm: Apocalypse)