Spoiler warning! This article contains plot details about events that occur later in the game.
Corey was first encountered, though not named for a short period of time, in the Beryl Ward, guarding the PULSE Machine with Taka and ZEL. He argued with Heather over her actions, ironically being told she "didn't come here to be lectured like you're my dad", and battled her while the player takes on his allies.
The plot here varies depending on whether or not all policemen have been found.
After Taka and ZEL have escaped, Corey attempted to do the same, but was stopped by the police force. They removed his hood and expose his identity to both the player and his daughter, who is emotionally shaken. Corey expressed that he had wanted to avoid such an outcome.
While the police were baffled that an upstanding person such as a gym leader would aid Team Meteor, Corey gave a cynical response about trusting authority, and assured them that there are more. After defiantly claiming the police force ultimately did nothing, he informed them that he would be at his gym and vanished.
After the player defeated Corey in the Gym Battle, Corey requested the player to go to Beryl Bridge, he would promise to answer the unanswered questions. At the bridge, Corey released all of his Pokemons and explained to the player his relationships with Team Meteor. After that he requested the player to watch over Heather for him due to the Ruby Ring she has making her a target for Team Meteor and proceed to throw himself off the bridge.
Corey's body was later found in the Lapis Ward by Victoria and Shelly. After the player arrives, Aster & Eclipse appear to confirm the death of Corey. Shade then appears out of nowhere and took the body away.
Later on in the game after the player obtains the Silver Card, you can read in his journal that he originally joined Team Meteor to sabotage them and get revenge on Sirius for killing his wife Elena.
Yo, Reborn City! What's up?! We're here with the Reborn Showdown giving you a look at the Leaders of the Reborn League! I'm your host, DJ Arclight, now on air!
Up today is Corey, the Beryl Ward's Poison Gym Leader!
An older man with more derision than a grandma at a metal show, this Poison Leader pours it thick with the pessimism.
Not a whole lot is known about the man, except that he frequently visits Beryl Cemetery. But who do you think that's for? Even I'm not sure. If you ask me, someone oughta go smack a smile to him. Life's too short to be moping around all the time, yanno?
Trainers, take old man Corey down a few notches for me, but when you do, be careful! His Crobat is a speed demo, and its attacks are no laughing matter. Take special care not to let it set up by keeping pressure on it with status moves or hard-hits. Perseverance will always win the day in the face of pessimism!
That's all for now, but remember, Trainers, Keep fighting with everything you've got! Hold your spirits high, and even you can defeat the Reborn League!