During New Republic Era, specifically in 34 ABY, a small battle took place on the Eravana, a transport ship operated by smuggling partners Han Solo and Chewbacca; this occurred within the Western Reaches.
Not long before this fight, Solo and Chewbacca successfully retrieved their stolen spacecraft, the Millennium Falcon, which Finn and Rey, First Order defectors, had used to flee the planet of Jakku. Their happiness didn't last long, however, as members of the Guavian Death Gang and Kanjiklub boarded the transport ship to collect the money Solo owed them. As Han attempted to negotiate with the boarding parties, Rey accidentally released three dangerous rathtars from the cargo hold. The rathtars rampaged through the transport ship, killing numerous gangsters and providing Han, Chewbacca, and the defectors with an opportunity to escape aboard the Falcon. They launched from the transport ship at lightspeed, successfully escaping and killing a rathtar that had attached itself to the cockpit.
Han Solo and Chewbacca, around the time they located their old vessel, were fulfilling a contract to move three incredibly dangerous rathtars to King Prana, who intended to outshine a competitor. Having lost the majority of his crew to the rathtars' appetites, Han's situation worsened with the arrival of the Guavian Death Gang, a criminal syndicate that had provided him with 50,000 credits for the task.
Instructing Rey and Finn to conceal themselves below, and also keeping BB-8 with him as insurance against their escape, Han greeted the Guavian representative Bala-Tik and his team, who were demanding the return of their investment after discovering that Solo had also made a deal with Kanjiklub through C-3PO. Despite Han's denials, Kanjiklub arrived, and the situation started to deteriorate.
Bala-Tik, noticing BB-8, identified him as the droid the First Order was searching for, along with two fugitives, and began searching the transport ship. Rey, in the ventilation shafts below, devised a plan to stop both gangs by sealing the blast doors in the corridor. Unfortunately, she activated the wrong fuses; instead of closing the doors, she accidentally cut the ship's power and opened all previously closed compartments, including the cages holding the rathtars. The freed beasts' terrifying cries echoed throughout the freighter, alarming everyone.
Bala-Tik, hearing the roars, decided to simplify matters by simply killing the two smugglers and seizing the droid by force. Just before they could fire, however, the Guavians were suddenly attacked from behind by one of the rathtars, which announced its presence by howling and grabbing two of the soldiers while the rest scattered or unsuccessfully tried to shoot it. At the other end of the corridor, Kanjiklub faced the same predicament with the second rathtar, while Han and Chewie seized the opportunity to flee, pursued by the rathtar that had been attacking the Guavians. They managed to evade the creature, however, by throwing an unfortunate Kanjiklub member into its mouth. Meanwhile, Finn and Rey emerged from the vents and ran through the corridors seeking safety. As Rey asked what rathtars looked like, having never seen one before, they turned a corner to find one in the process of devouring three gangsters and quickly retreated, only for the third rathtar to grab Finn and drag him away. Rey briefly gave chase but quickly realized that she had little chance against the creature even if she caught up to it and instead managed to free Finn by closing a blast door on the tentacle holding him.
Simultaneously, Han, Chewie, and BB-8 were trapped against a blast door to the hangar by some Guavians, who managed to wound Chewbacca with a shot to the arm before they were defeated. Using Chewie's acquired bowcaster to blast open the door, they met up with Rey and Finn and boarded the Falcon to escape. While Finn attempted to care for the injured Chewie, Han and Rey prepared the ship for takeoff, which was complicated by a rathtar that had attached itself to the cockpit window and was trying to bite through it.
Deactivating the compressor preventing the hyperdrive from engaging, the Falcon then jumped to lightspeed from within the hangar, with the extreme acceleration literally tearing apart the unfortunate rathtar, which was still clinging to the ship. Witnessing the escape, Bala-Tik informed the First Order that the droid they sought was with Solo.