I may a bit late with to reply in this thread, but better late then never.
So here´s my character:

Name:
I haven´t thought of an adecuate name so far, since my thoughts were dwelling only about what the entire idea of this character is and not how he should be called.
Team:
This character is supposed to be a member of the Strawhats. He would be the “priestâ€? of the ship. Donâ€
t shout at me let me first explain what I had in mind.
The Age:
I think having him somehow around 21 years would be fitting for a young priest. He would be a little older then most of the Strawhats but still a youngling who has much to learn.
Basic Idea:
Labeling him as a priest is not intended to mean that his purpose for sailing is a crusade or that he´s some sort of missionary. NO! What I had in mind while creating him is that in pirate stories there´s much story material based on mystic powers. For example, ghost ships, cursed treasures etc. And my priest is actually a character who could deal with such things.
My character is actually more some kind of priest-monk-medecineman-magician-combo.
Let´s say if the Straw Hat´s should ever encounter a ghost pirate crew, he would be the only one to defeat them because the strong Luffy, Zoro and Sanji might be, they can´t kill dead people. 
His Aim:
I always had the idea that there´s more to the Devil Fruits then we know so far. So this character´s aim would be to find the origin of the Devil Fruits. Since he is a priest and many people get hurt by evil DF users his aim would be to search for a way to either counter or permantentally remove the DF powers from an evil DF user.
I didn´t think of an adecuate backstory so far, but I think in his past something must have happened to make him wish to be first (the best) priest to stop DF´s powers being used to hurt innocent people.
Skills:
Now for the interesting part. When it gets to fighting the opponent then he is the only one of the Strawhats who could defeat a ghost or a demon. Luffy, Zoro and Sanji couldn´t do anything against them because in my book ghosts and demons can´t be harmed by mere mortals. The weapon of he uses would be (hold your breath) a fan!
But what would a Strawhat Pirate be without some large flaws? His would be his fighting skill. While as a priest he has great potential to defeat ghosts etc. his human fighting skill would be somewhere between Usopp in the Kuro arc and Chopper in the Drum arc. That means whenever he fights normal guys he would get beat up which brings me to my next point…
Character:
Among the Strawhats he would be the very calm voice of reason like some sort of a ships councelour BUT of course with the temper of a true Straw Hat Pirate, meaning even he would kick Luffy´s ass if he bother´s him too much. But when this would happen he would do it in some “religious� kind of way. For example punching Luffy while saying “May your sins be forgiven� (or something like that).
He would be one of the “wiser� crewmembers, but at the same time he would have a very bad sense of knowing his own limits. For instance, if the Strawhats get into a fight with lots of opponents he would bravely follow Luffy, Zoro and Sanji into battle only to get the crap beaten out of him, because he´s completely useless when it gets to fight humans (remember fighting power between Usopp and Chopper). That would be one of his comedy parts.
Other then that I intend him to be the cute boy of the Strawhats, meaning that the ladies of One Piece tend to find him hot (though they wouldn´t molest him like Sanji does when he sees a hot lady). But since he is a young priest he wouldn´t even care about how attracted the ladies feel towards him, which makes him only sexier to the female gender. This would make for great interactions with Sanji, since he would always be pissed that a guy who doesn´t care for women gets all the attention.
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Well that´s it actually. I don´t think that I´ve forgotten something. Actually I when I first thought about the character I thought he would be a possible future creation of Oda. But then my own idea of him became more and more developed until I realized that it is just wishful thinking of me to have such a guy in One Piece. So I have to admit this guy´s definitely just my own creation and nothing that we will ever see in OP.
As far as the picture above is concerned. In order to have a One Piece character I thought it would only be fitting to include “original� Oda artwork. The pic consists of two characters from Oda´s oneshot “Ikki Yakou�. The body is from the main character, a young unexperienced priest (sound familiar?).
The head belongs to a guy who plays the forrest god. That´s the reason why the face and hair don´t really fit the clothes designwise. Actually I just made this photo as visual reference for my character. You should all see the basic idea behind the character´s design. He should have an attractive face, but a priests outfit. Here´s the some more pictures of the forrest god´s face aswell as the true pic of the young priest.


Well thanks everybody for enduring so long to read through this post. Hope you liked any of my idea´s and some feedback would be appreciated. 