The planet Libertia was once known as “the planet of death”, until humanity built three giant mirrors and created what seemed like an ideal land. It is on this planet that Professor Grace and his granddaughter Alcia live peacefully… until their home is attacked by Guild soldiers looking for the professor and for Legaciam – a special Armor that can resist extreme heat, allowing it to go to areas where humans would not survive normally. Alcia, who was at the time piloting Legaciam in order to help her grandfather with the testing, manages to get away… barely. But the Guild is determined to get Legaciam by any means necessary…

(Source: Anime News Network)

Spin off of Akinori Endo's novel, 'Warrior of the Tower: Relic Armor Legacium'.