We know that the strength of Heartless are based on the hearts they steal. But, perhaps as a theory, what if they evolve as they steal more hearts, with the stronger Heartless being older than others, after having survived long enough.

So, basically, a Displaced as a basic Shadow Heartless. Acting as a sort of Anti-hero in a corrupt Equestria. Like a more murderous batman that kills those that are corrupt. But also being a Heartless that actually fights other Heartless, trying to limit the victims to those that deserve it.

what's a heartless?

The heartless are a type of enemy from the kingdom hearts series. below is a description from the wiki

The Heartless are living beings, whose hearts were corrupted by darkness, and they play the roles of the "common enemies" Sora and party must defeat. They exist for no other purpose than to consume hearts, be it the hearts of other living beings or even that of entire worlds. The hearts that Heartless take from others become Heartless themselves. There are two types of Heartless, the shadowy Purebloods which are naturally created Heartless and the Emblem Heartless created by Xehanort and Ansem's apprentices.

4618210
Now that's interesting a protagonists that protects the people from his own kind while controlling his instincts.
So if Candace becomes a heartless how bad would a situation be. May the protagonist becomes the form of ansem aka Xenahort heartless. Wait I can imagine if during the years he gain ability to control more than one form though it has to be pure blood heartless.

4618271 Yeah. But likely custom Heartless forms beyond the first Shadow form, eh?

4618260 Close. But it's not that the Heartless's hearts are corrupted by darkness. No, they are born from the darkness. They're living darkness. They have no physical hearts. But, Sora kept his sense of self while turned into one(not easily, but still). So, why can't someone else?

Another possible result is that as he gains more control of his powers, he could learn to control the Heartless that are weaker than him. But, that's just an idea. But, in turn, that could mean that it's possible he could have to suffer having to resist orders from those with hearts dark enough to be stronger than him. Or something like that. Since he'd be a sapient heartless, normal rules don't really apply, so lots of creativity could be used there.

4618234
Heartless are main bad guys from kingdom hearts series since they are born from darkness or the darkness of people's hearts. To permanently kill them requires a keyblade or similar to it. They travel to different worlds by darkness. (human versions will either disappears or corridor of darkness) They convert people by eating their hearts

4618210
So sort of like the monsters in Bleach then? Which would also leave room for someone's natural affinity to start higher or lower than someone else. Though of course I would mean natural heartless rather than manufactured, though it would stand to reason a regular heartless might incorporate some functions of the manufactured variety if they took a mind to it since they have the same base components.
Also, I don't think you mean a murderous (i.e. killing for illicit gain) Batman, that would be a straight up villain and you would be better off just calling him Owlman at that point, perhaps you meant a Batman who actually kills people who are murderers themselves rather than sending them off to an institution where they are treated as a special class above repatriation until they find a way to escape again so they can murder again.

4618385 That's essentially what I mean, what you described there. I guess in a way it could be considered like the Punisher in Marvel too. Kills villains, yet protects the innocent.

4618412
An interesting concept then, certainly having a heartless that keeps it's mind but not the shape of it's original form has some merit ranging from shadow to neoshadow to Darkside, though depending on how you want to play it you might also shape it into a pony (like Riku does with Shadow Sora). As for other characteristics, it could be rather easy to go overboard with powers from manufactured Heartless, at least by my own reckoning, but as for a stable power-source, you could certainly make your way to the Crystal Empire for their special rock and Cadence besides with her love magic, though of course you could also make an OC who has much the same (just not as powerful as an alicorn) or even be a friend or even a competitor of Changleings when it comes to consumption of love. It would certainly be rather cute to see a sickly Shadow skulking in the darkness of some forgotten corner of a hive feeding off of bits of love because the eating hall is too protected or what have you.

4618495 lol That'd be interesting. (I actually have a blog with my complex changeling headcanon if you want to check it out.) Though, there's more natural heartless than just the three you mentioned. There's Invisibles, Darkballs, a lot more from 358/2 Days, Dark Thorn and possessors from Kingdom Hearts II, and that one massive one Aqua faces in Birth By Sleep Final Mix. And it's quite possible such a Displaced could gain his own custom forms as well. Not easily, mind you, but possible. Perhaps having the forms available depend on the personalities of those whose hearts he consumes.

4618210 I'm sorry but all I'm thinking about is the basic Heartless and how much I want to hug one.

4618527 XDDDD Nice. XD

4618210 If you end up writing this, let me know. I think some interesting things could happen if he ever crossed over with my displaced.

4618582 Ah. A Keyblader displaced, eh? Makes me surprised someone hasn't done one on Lingering Will yet. Ah well. As for whether or not I make this heartless displaced fic... we'll see. Got a major project I'm trying to finish first, and then got two other displaced type fics to start. If you have Skype, we could discuss them if you'd like.*shrug* Besides, I'm a bit bored, despite the chores I'm multi-taskin' with. XD

4618601 An interesting proposal. I'll PM you my Skype address later. We'll talk. Should be fun!

4618620 Alright.^_^ I'll be home all day, though some of the chores I have to do may prevent me from responding right away. Only got a few things left to do though, thankfully. One of which is lengthy, but still.*shrug* Should have plenty of time to talk. Up to you when with the exception of what I just mentioned in regards to my chores. ...and I am way too talkative sometimes. XD

4618624 well this should be interesting I'm willing to cross over this idea as well with my own keyblade displaced. Also make sure the heartless arrives at the bramble weed incident. The tree of harmony can act a lot like the cornerstone of light I figure and with the magic getting drained should allow heartless to appear in equestria. If you want a oc heartless I got one you might like. It's shaped like a fox with fire abilities. I will leave the name and varient to you if you wish. It's a concept I'm planing for my own fix a key in equestria.

4619152 Well, I was honestly just putting this up in the air for others to take. Buuuut, I might write it.

But now, I see there's two displaced as Sora. Would be hilarious to have them cross over together. One of those "Sora?" Both: "Yes?" XD

I have plans for other fics to do, though not till a major project is finished first. One is a super complex single Displaced, though displaced through the third method(first method: Merchant, Second method: Discord's power lottery, third method: another displaced), while the other that I have in mind is a multi-displaced as a group tricked by the merchant.

4619170 my character goes by james del light just change the eye color to green and you got him. Makes it easier to tell them apart.

4619568 Ah. Understandable.^^

4618210
A Heartless doesn't gain strength by consuming hearts, their strength originates from the heart from which they were born; the darker the heart, the stronger the Heartless. This is why Sora was a lowly shadow, he had very little darkness in his heart, if any. Heartless don't actually consume hearts at all, the hearts of their victims instead become new Heartless. This is not to say that Heartless can't become stronger or change forms, just that they don't do it by eating hearts.

There's an excellent non-MLP Heartless SI fic that sounds a lot like this concept, and if you're looking for ideas, you can check it out here.

4618601

...there is one, actually. For Vanitas', at least. It's also a cross with Fallout:Equestria, but just after the shit hit the fan. Can't remember the name off the bat, but the guy's mute unless he used Twilight's Pipbuck to type out something. Then he 'sounds' like Microsoft Sam. Interesting concept and execution, and a little close for my comfort.Seeing as I plan to use Vanitas myself...

4620041 We don't know this for sure. We know for sure that the starting heart they consumed is what determines their strength. But, too little is known about the Heartless to rule anything as a guarantee on how they work.

4620459 lol Well, Vanitas is quite different, since he can summon Unversed from the start, eh?^_^

4620478 That is true, and that's what makes him so freaking terrifying. According to the wiki, as well as the novels for BBS, every time an Unversed is 'killed' it causes incredible physical pain to Vanitas, like you chopped off his arm. The fucking terrifying thing about that is it that his frustration and rage that he feels as a result goes into the creation of another Unversed. Meaning that the more you destroy, there are literally three more to take its place.

4620495 So basically, it's an alteration of the power where the more damaged an individual becomes, the more powerful they become. A rare but terrifying ability, that. The only way to effectively fight such a foe is to get them to wear themselves out.

4620502 Consider the fact that if he wanted to, he could throw out boss Unversed like the Iron Imprisoner, the Mimic Master, the Trinity Armor, and a whole slew of scary motherfuckers.

4620551 lol I know. Just cause I said it's the best strategy doesn't mean it'd be easy. XD