My Little Light (Reader x Gray x Natsu x Lax...
You've been friends with Gajeel for a really long time. You always played together when you were kids, and always adventured through the continent of Fiore. Eventually, the master of Phantom Lord had starting asking Gajeel to join his guild. He would always refuse the offer saying "As long as I have you Shorty, I won't fall to the dark side." Which was true. For years Jose prodded at Gajeel, trying to get him to join. Yet, one day when he woke up, you were gone. He lost his light and fell to the dark side.
He's in Fairy Tail and you're finally back on the grid. When you arrive at the Fairy Tail guild, you're greeted with a familiar face. But how will he respond to you resurfacing after the past twelve years? You join the guild and make many friends. Not to mention immediate respect from Titania, Erza Scarlett.