Your experience with homebrew character concepts

Hey guys, I am very new to DnD but have been cooking up a character idea that I would LOVE to play, yet at a first glance, I am seeing some issues with the concept, which discourages me a little bit. I would LOVE to hear from your guyses experience with this (or similar) kinds of things as well as whatever input you have. Just please dont rulehammer me too brutally, since I am (as stated) fairly new to the system and tbh a bit insecure about my own works and ideas. Criticism is appreceated nonetheless!

The thing in question is called "horrifying secret" and is basicly somewhat of a perk added to a character.archetype I cooked up, if that makes sense terminologywise.

It serves as a canvas for the character "Redfort of Astoria" (a country that would not exist anymore in the current setting), who appears to be a human fighter, but in reality, is blighted by a curse of undeath that stripped him of both his flesh and humanity centuries ago, while "living" in complete ignorance of the fact. He does not know fear, hunger, fatigue or any other mortal toils, while always being in an optimistic, if not naive mood, explaining his lack of mortal needs by believing himself to be some sort of blessed warrior, "fueled by duty and nourished by rightiousnes". On the surface, his motivation and drive are smiting evil where ever it may appear and being an honorable "human being", sworn to protect the innocent at all cost, while in reality, his main goal (though he does not see it himself) is ridding himself of his own existence, regaining his humanity and freeing his soul from the eternal struggle he is stuck in, caused by constant rebirth after being destroyed (he basicly reincarnates into a new, undead body and "resets" to where he started every time, including memory loss and all). He unknowingly longs for mortality and the mountain of experiences that come with it, including true happiness and love, but also things like pain and sadness, which he cannot experience until he remembers.

He can only "feel" happiness and satisfaction after completing a deed, rekindling his humanity bit by bit and also bringing back his memories (which is tied to leveling by bringing back parts of his old skills as a warrior).

Apearencewise, he is basicly a suit of armor, propped up by magic, which hides his scelletal apearence behind the facade of a warrior who never takes his helmet off in order to be "always ready for duty". When he looks at himself, he sees nothing but heroism and excelence, while in reality, his gear is old and far beyond its prime, adding to the fact that he lives in "fairytale land", not recognizing that he is navigating a world he neither sees as it is, nor truly belongs in. To him, purpose lies in saving the next damsel in distress he can find and slaying the foulest beast around. Saving the day is his drug and only way to salvation.

There is a backstory for it all, but I wanted to try and explain the concept first. I hope you guys see it as more than snow-flaky nonsense.

It sounds cool, but I don't really understand how anything the character doesn't know matters? How can he desire something he doesn't know about? Why would him being a reborn undead but having no knowledge of being such matter in the game? How would it affect his decisions if he doesn't know about it? For that matter why does he make attempts to hide his appearance if he doesn't know he's a creepy undead being? 

You also should run this personality idea past the other members of the party, I could imagine some players/DMs not being thrilled about playing with a character who has no investment in the rest of the party and is completely lacking in personality. While other tables love character that just want to progress the story and don't go off on sidequests or just mess around.

In general when coming up with a character for D&D, you don't need a long complex backstory. You need the bare minimum backstory to answer these three questions:

(1) Why is the character willing to risk their life to go on adventures?
(2) Why does this character want to care about and work with the rest of the party?
(3) What does the character need to change about themselves in order to be truly happy?

For your proposed character I see answers to two of these: He risks his life to go on adventures because he is addicted to it as it is the only thing that brings him satifaction, and he needs to regain his humanity in order to be truly happy. So you just need to answer, why does he care about the other members of the party and want to work with them - including to the point of putting aside his desires to pursue something the other members of the party want to do.

PS you don't need any homebrew to achieve this character concept. Sounds like a classic Paladin archetype or could be a straight Fighter with using the Reborn species option (or even a reflavoured Warforged). 

Thank you for the quick response! You raised very good points about certain issues with the idea!

Especially the reborn-species-option (which i completely overlooked for some reason) would make the whole concept MUCH easier to do and streamline it quite a bit, including the whole appearance-issue! The more "normal" his condition is, the more points can be taken out. Otherwise, him hiding his true nature can be explained by hostile experiences from the past. If people throw rocks at you on sight, you learn to disguise yourself, no matter your own reflection. Redfort is a dreamer, but not an idiot. Mostly.

As to your questions: 

The pursuit of regaining his forgotten humanity is mostly a subconcius one. Imagine a dreamer slowly waking up and coming to his senses, trying to fill the void in his heart with other things than the fleeting bliss of a job well done, while becoming more and more of a person as time goes on and reality sets in. Turning his blind heroism into actual heroism. It's absolutely possible that I am overthinking this and could just make him a magical bone puppet who wants to become a "real man" instead.

As to caring about the rest of the group, this is fairly simple to answer. Redfort would view the group as his allies at first, a "rag-tag band of ruffians" in need of his glory and excelence (a bit arrogant, I know), but would grow attached to them overtime by witnessing their own struggles and turmoil and kind of learning from them what it means to be a mortal/true hero. The growth of the character as a person is basicly hard-wired into the concept and is supposed to bank on the group side-questing as much as possible. It's really not that different from the classic "we met as strangers, but left as family"-stereotype. But as I said, I lack experience when it comes to actually playing DnD and experiencing the classic group dynamics at the start of the plot. But I can deffinetly see this concept not being for everyone and would 100% introduce it first. Asking you guys is kind of dipping my toe in the scene, if that makes any sense.

My main experience comes from playing WoD back in the day, where everyone is in it for themselves, more or less.