Roxita was a commander of the Capitol Guard during the Last Great Time War. He was assigned to the guard detail for Cardinal Ollistra when she travelled to Synthesis Station to assess Doctor Eva Morrison's work on artificially augmenting the Vashta Nerada for medical, military, and mining use. When the facility's security protocols were temporarily shut down, Roxita initially assumed that the Eighth Doctor was responsible.
He soon discovered that the actual culprit was Dendry, a technician who had tried to steal some of the Vashta Nerada samples. He and his squadron opened fire on Dendry’s ship but accidentally destroyed the canisters holding Vashta Nerada hatchlings. They then devoured Dendry and most of Roxita’s squadron. Soon, only he and his Captain were left and they made it back to their Battle TARDIS. However, that too was infected with Vashta Nerada and his Captain was devoured. He then left the TARDIS and met up with the Doctor’s group.
With most of the station staff having evacuated, Roxita, the Doctor, Ollistra and Doctor Morrison were able to retreat to the Doctor's TARDIS, but the Doctor realised after they dematerialised that a small group of Vashta Nerada had hidden in Roxita's gun. Forced to retreat to the secondary console room, the Doctor suggested that they wear the spacesuits in the console room and dispose of the Vashta Nerada by dematerialising the TARDIS from around them, leaving them in deep space while the creatures were expelled into the Time Vortex, and programming it to materialise a few metres away. However, when there were only three suits in the console room, Roxita chose to sacrifice himself so that the other three could use the suits, reasoning that it was his duty to protect Ollistra, the Doctor was Ollistra's best chance at survival, and Eva was an innocent victim.