Fairy Tail and Fate/Grand Order Challenge

Have any of you heard of the fanfic Opening Dangerous Gates by LadyD0544? It was a crossover between Fairy Tail and Bleach. Basically, after the Grand Magic Games arc of Fairy Tail, Lucy Heartfilia acquires two new Celestial Spirit Keys. One is black and summons a different Shinigami every time it is used. The other is white and summons a different Arrancar every time it is used. Lucy ends up having to use them a lot to fend off demons from the Books of Zeref. Every time the Keys are used, they summon the right person for the job, like when they summon Tier Harribel to deal with a sea demon (her control over water was superior) and when they summon Toshiro Hitsugaya to deal with an army of tree demons (ice kills plants). Of course, it isn't that easy. Just like a regular Celestial Spirit, Lucy is drained of strength the longer her summon is out, and there are times when her summon refuses to cooperate. There was of course lots of development with the other characters, especially with Gajeel and Levy's budding romance. It gained a TV Tropes page, but sadly, the fic hasn't been updated since 2015.

My challenge is simple: Write a story similar to this one, except Lucy summons a Servant each time the special Key is used. If you want, Lucy could have one Key total, or she could have one Key for each Class like Saber, Archer, Lancer, etc. Emphasis should be partially on awesome fight scenes of course, but it should also be on the interactions between the characters. Can you imagine how the Fairy Tail characters would react if they met Achilles, Cu Chulainn, Spartacus, Minamoto no Raikou, Jeanne d'Arc Alter, EMIYA, Jack the Ripper, Edmond Dantes, or Scathach? I've been wanting to write this myself for a while, but I just couldn't figure out how to start.