You got the whole thing wrong. Natsu,erza,lucy, and some more realised themselves that their magic power has remained the same as 7 years ago while the rest guys of the guild could match up to their strength.So they decided to train so they can get it back, but lucy's spirits played a joke on them so they can bring up a feast for their return.The thing is that 1 day in the spirit world is 3 months in real time.So after they came back to the real world they met with jellal, the one with emotion links and the woman who controls the time and offers them a solution to take their magic power back to maximum in return huge pain. They take the challenge, and get their magic power back. The story continues while some guilds are trying to take over fairy tail's establishment then natsu and his team that they were said to be disappeared came back and kicked their asses. But for their misfortune they learn that fairy tail guild is now one of the lowest guilds in Fiora, and so on.... Some episodes after that they learn that there's an event going on for the strongest guilds in Fiora so they decide to take part and get their way back to the top as the strongest guild in Fiora. Bored to write more, watch the mangas.