Three years after the First Formic War, Rimas was a member of Mazer Rackham's breach team in testing WAMRED technology for use in war against the Formics. In one exercise, Rimas was in a capsule heading for a derelict ship that was being used as a fake Formic ship. After placing his Gravity Disruptor, he took out some simulation Formics and ended the exercise.
After the mission, Rimas mentioned that there was no cover from the Formics and that the team needed cover. Upon that note, Rimas started theorizing a way that the team could bring shields with them. After words from Mazer, the breach team started trying to develop an idea for a shield based off the Nan-Ooze nanomachine technology.
Later that evening, news came from the Hegemon Ukko Jukes in a vid, announcing that one of the eight Parallax Telescopes, Copernicus, was destroyed by a Formic fighter ahead of the main alien fleet. Rimas discussed the news with the rest of his breach team.
Some days later, Rimas and the rest of the team set out to test the live Gravity Disruptor charges. However, one of the four cubes was faulty; Mazer radioed to mission control asking to abort the mission, but his request was denied. Instead, he used contingency Beta, where three cubes would align into a triangle. The resulting explosion ripped the test ship apart, sending shrapnel in all directions. One piece sliced into Shambhani's calf, creating a gaping hole in his suit. His suit sealed itself, but abandoned his leg from the knee down. The team was taken back to the station in a medic ship, but there was little chance of saving Shambhani's leg.
Rimas was reassigned from WAMRED to a cargo ship with 100 other special-ops marines, due to the incoming Formic fleet. After arriving at their target asteroid of Castalia, Kaufman was assigned to the squad that would infiltrate it, along with Rimas, Mazer, and a cadet named Bingwen.
Two days later, the breach team was ready to go. They planned to kill the crew of the Formic Miniship, collect the bioengineered "bugs", and then send in Bingwen once the threat was eliminated. Kaufman and Rimas followed Mazer into the asteroid after he cut a hole in the resin shell and investigated the surface. After surmising that there were no Formics present above-ground, Zembassi sent in Bingwen. Mazer ordered Kaufman to leave and transfer his supplies to Bingwen, and then wait in the shuttle craft, while Rimas would stay with Mazer. After realizing that Mazer and Rimas could not fit in the tunnels, Bingwen suggested they give him their supplies and wait out in the shuttle for Bingwen to finish investigating. After Bingwen found the Hive Queen daughter-general and blew the asteroid's atmosphere, Kaufman, Rimas, and Mazer rushed in to find Bingwen still alive but unresponsive. They took him back to the ship to recover.
Rimas was shown to have a sense of humor, when he called his breach team "guinea pigs".