Lia, or Liandra Chiaria is the twin sister and best friend of Ithan Chiaria. The two have been traveling and living together for most of their lives. Lia shares all historical dates with Ithan, in birth and significant life events. The only murky part of Lia's history is during the Imprisoning War, in which she is not present, yet Ithan is.
Lia and Ithan were both alive during Season 1 and 2 of Interloper War, with only Ithan showing himself. Both have worked together to travel back in time, as part of a surveiilance of Polaris and his trajectory through time.
Lia and Ithan were both reintroduced in the Six Months Later Part I chapter of Interloper Season 3. Lia was then dormant until Evening 2 when she decided to join up with the resistance forces.