Written by: The Inquisitor
So, Brandish knew Layla. When that was revealed, I was immediately suspicious. Brandish looks like she's somewhere between 18 and 25 years old, and Layla died 15 years before the current arc, this would mean that she was 3-10 years old when Layla died. This fact makes it very unlikely that the two of they could have met, let alone have had a "long and irritating" history. That quote by Brandish brings up another point, what could the kind-hearted Layla Heartfilia have done to a ten year old that would cause her to have a grudge against Layla's entire family? There are a few possible answers.
|Let the confusion begin.|
X792: Current year.
X784: Tenrou Team disappears.
X777: Layla Heartfilia dies of an unknown illness.
X767: Lucy Heartfilia is born.
X764: Layla Heartfiilia retires from magic. 
X748: Layla Heartfilia is born. 
The first theory for how Brandish and Layla are connected was created when I thought about everything that happened during the years that aren't stated in the timeline. At some point between the years X748 and X764, Layla worked for a merchant guild known as Love and Lucky. This guild is where she met Jude, and where she became pregnant with Lucy, after which both Jude and Layla left the guild, and Jude eventually founded Heartfilia Konzern. In these facts, there is one of two things: a massive contradiction, or a massive oversight .
Layla supposedly became pregnant with Lucy before Heartfilia Konzern was founded. However, when the year of Layla's retirement was revealed to us by Leo and Capricorn, with that reveal came a flashback, the year of the flashback was X764, three years before Lucy was born. And the location of the flashback was Heartfilia Konzern. This can only mean one thing, Lucy was Layla's second child. 
Brandish being Layla's daughter would explain the resentment that Brandish feels toward Lucy. Brandish could be furious because Layla, for some reason, abandoned her, or maybe she's jealous of Lucy, or maybe it's a mixture of both.
|Speaking of Capricorn, why the hell did Layla think giving his key to this guy was a good idea?|
When I first created this theory, I thought it was the most likely to be true out of all of them, but then I realized that there is a lot of evidence that might disprove this theory. First, Lucy's name was inspired by the broken Love and Lucky sign, when Jude and Layla left the guild they noticed that the K was missing, and they decided that if Layla's child was a girl they would name her Lucy. In this theory, Brandish is the older sibling, and her name is obviously not Lucy. So, unless Brandish is a trap, she is most likely not Layla's child. 
And second, the evidence to support the theory is not concrete. Leo and Capricorn never specifically said X764, they said "20 years ago" and they may have been rounding up. If Layla actually retired 15-20 years before the Tenrou Team disappeared, then she could have retired after Lucy was born.
Despite the unlikelihood of this theory being correct, it was the only answer that I could come up with. I couldn't think of any other way that someone as young as Brandish could have met Layla. The obvious solution to that problem is that Brandish is older than she looks, bet even then, it's unlikely that she could have met Layla. I doubt that they would have been able to meet after Lucy was born, or when Layla was working at Love and Lucky. In order for them to have been able to meet, then Layla would also had to have been older than we thought. That would increase the possibility of them meeting, but it also makes it more difficult to determine how they met. Since the time period that they met in is purely theoretical, we have almost no details on what might have happened during that time.
|If that is the case, that date of birth is fake. You sit on a throne of lies Hiro Mashima. And to anyone who noticed, yes, that was a quote from Elf.|
Layla was familiar with the One Magic. Whether or not the One Magic is common knowledge has never been clearly stated in the manga, but even if it is common knowledge, she knew enough about it to make her own theory on what it is. This fact links Brandish and Layla with a common factor: Zeref. What kind of situation could Layla have been in that would involve both Brandish and Zeref? My answer: she was a former member of the Spriggan 12.
Layla being a former Spriggan would greatly increase the chances of her having been able to meet Brandish. And it could also explain why Brandish has such a vendetta against Layla. Maybe Brandish was a member of Layla's squad, and Brandish, who may have idolized Layla, is angry about the fact that Layla left. Or maybe instead of simply leaving, Layla betrayed Zeref and company. Maybe the betrayal resulted in the death of someone close to Brandish, that would explain why Brandish doesn't just have a grudge against Layla, but against her entire family.
Of course, this theory leaves a lot of questions unanswered, such as, why would Layla work for Zeref? How much did Jude know? Why would she betray them? There are more, and as of right now, I don't have a definite answer to any of them. Layla's past is a mystery, and the solution that clears it up probably won't be revealed for a good while. Do you have any ideas? Do you see any flaws in this theory, or do you have an unrelated theory that you want me to take a look at? Let me know in the comments.
|Brandish, it took Erza and a fucking magic cannon to defeat Ajeel, and you get knocked out in one hit by Cana. I'm disappointed.|
1. Chapter 224.
2. Chapter 68.
3. Chapter 130.
The Inquisitor is an autistic otaku with little social life. If, for any reason, you need to contact him the preferred method would be to email him at Steven.firstname.lastname@example.org, or you can go to his ask.fm account: ask.fm/guardiansandfollowers. He likes to get straight to the point.