Tillian and his partner Kam discovered a damaged EX droid and managed to repair it enough to find out it was EX-8C who belonged to Outer Rim Expedition Two-Five-Two. After discovering a distress call in the droid's memory banks, Amos suggested they contact the Pathfinder team they were working with so they could investigate.
As they entered the atmosphere of Aubadas, Tillian was able to contact Obik Dennisol on the surface and agreed to meet the team at their ship. He and the rest were led by the native Katikoot to the ambassador's lounge in the capital city of Diurna where they waited for the Jedi to finish their meeting with the leader of the Katikoot. He marveled at the technology of the native species, including their hoversleds. The engineer enjoyed a glass of Hibinacho juice but the high sugar content made him jittery. Silandra Sho returned and informed the rest of what the Katikoot told her about the other Pathfinder activities. Tillian was hesitant to go to Gloam to investigate the missing team due to the danger, and Sho instead requested he and Kam look at the Katikoot's communications systems to see if they could figure out why there was so much static and interference.
Tillian went to the systems hub in the center of Diurna to look at the equipment. He told Kam he thought that it was strange that local communication was being disrupted. Kam suggested to Tillian that they might be looking at the issue the wrong way and perhaps it wasn't an equipment failure but a deliberate sabotage. Excitedly, Tillian went to the main communications relay and studied the equipment and mentally mapping the circuit relays. He noticed a strange looking power hub and requested that GT-11 remove it. As the astromech used its arm to pull off the casing, Tillian noticed it had a blinking circuit on it and realized it wasn't an actual power hub. Unfortunately, the discovery of the device led it to shutdown the entire system and terminate all the power in the city. He observed as Kam examined the communications system. Tillian became nervous that the Katikoot might throw them in jail for breaking the city's power supply, but Kam reassured him. After Kam's attempted fix briefly restored power before shorting out again, Tillian asked to replace Kam to see if he could fix the system. He tossed aside the fake power hub and did some rerouting on the system. Standing back up, he told Kam to press a button on the console that restored the city's power supply.
When the Pathfinders returned from Gloam, Tillian joined them in celebrating the end of the Eiram and E'ronoh War.
- Star Wars: The High Republic Character Encyclopedia