I grabbed this specifically because it was an attempt to mimic magic in the Fairy Tail Anime.
The sub-class is excellent. Just about everything I agree with thematically and it seems balanced. There are a few pieces I am not sure about how well they balance in actual play as I have not used it to build a character I have actually run through adventures.
The basic ability is to have one stored item per fighter level and that means a maximum of 20 weapons or armors stored. That number seems a decent amount without bein overly difficult. I am glad the author didn't try to tweak the 3 item attunement requirement, as that would cause a lot of difficulty in the rules as written.
The 7th level ability seems a little odd, at least for the part where you can swap weapons. At 3rd level you can store as a "free" action and retrieve as a bonus action, so in theory you can already do that. Otherwise it is a good place to introduce the storing of armors and outfits.
The remainder of the abilities are small tweaks to the Eldritch Knight abilities or sufficiently comparable.
In addition, there are eight new spells. Most seem reasonable and comparable. The Ethereal bonds spell and Frost Whip spell seem a bit strong for their level, but it would be good to see them in actual play. It is also good to mention that even though they are third level spells they are received much later than the wizard would receive his, so perhaps not a big deal.
[5 of 5 Stars!]