FN-2187 served under Captain Phasma and, as a cadet, alongside fellow troopers FN-2199 ("Nines"), FN-2000 ("Zeroes"), and FN-2003 ("Slip"). FN-2187, known to his fellow troopers as Eight-Seven, was seen by his comrades and superiors as an ideal First Order stormtrooper, and consistently scored top marks as a cadet. Finn was also once in charge of sanitation duties at Starkiller Base.
During his time as a cadet, Eight-Seven and his fellow troopers underwent a training simulation in which they assaulted a New Republic bunker, with the intention of destroying a heavy repeating blaster manned by Republic soldiers. During their advance on the bunker, Slip fell behind—a common occurrence—and Eight-Seven intended to rescue him. Over the objections of Zeroes and Nines, who wanted to complete their objective and felt that rescuing Slip would lead the Republic to take them all out, Eight-Seven ordered them to rescue their fellow soldier. Eight-Seven sent Zeroes and Nines in different directions in order to divide the Republic's attention, while Eight-Seven himself went for Slip and successfully rescued him. Though Zeroes and Nines were pinned down, their diversion gave Eight-Seven a clear path into the Republic bunker, into which he threw a grenade and destroyed the blaster before the Republic could react to his attack.
The simulation was monitored by Captain Phasma and General Hux. After the training session ended, Phasma spoke to the troopers and told them that their performance was adequate. Each was given a review of their performance, with Eight-Seven being commended on his kill rate and the completion of his objective. She further said that his fellow soldiers should follow his example. The other troopers were dismissed, but Eight-Seven was ordered to stay so Phasma could question why he rescued Slip, as it was not the first time Eight-Seven had to help him. Phasma ordered him to stop, as she said the First Order was only as strong as its weakest link. Rather than fixing the problem, Phasma said he was allowing it to persist and weaken the group. Phasma sensed hesitation on his part, but he assured her that he would stop helping Slip.
Following this incident, FN-2187 and his fellow troopers were deployed to a mining colony in an artificial asteroid field known as Pressy's Tumble in the Outer Rim system of Pressylla. Captain Phasma informed the Stormtroopers there that the purpose of the visit was to 'restore order' after Republic agents had infiltrated the mining operations, sabotaged equipment and created dissent among the miners there. Upon arrival, Captain Phasma took FN-2187's unit to a room of negotiators. Captain Phasma then gave the order that the troopers execute the negotiators. FN-2187 aimed his rifle at an Abednedo negotiator, yet couldn't bring himself to shoot—Slip attacked the negotiator instead. Upon returning from Pressylla, FN-2187 and his fellow troopers were officially recognized as full-fledged Stormtroopers. Captain Phasma decided that FN-2187 ought to be deployed in an upcoming battle in Jakku, thinking that he would understand what it meant to be a Stormtrooper and fight back when brought face-to-face with those attacking him back.