Ok I suggest you read this, its kinda important . So I'll be explaining your devil fruit, the death-death fruit .

Its a cursed devil fruit that you ate when you were young . you can stay in the water for maximum 5 minutes without losing all your strength (only loosing 70%) . But thats it . You cant swim and you will drawn and die . 30% isn't much... only moving around a little and managing to talk. ..

Immortality : you cant die or get killed normally . Similar to brooks devil fruit , but a logia , But you didnt die before . However your weakness like any other is water and sea prism stone .

Soul summoning : you summon souls/ghosts to help you with things like finding something or scaring people off or etc.

Soldier ghosts : you summon a ghost army helping you fight .

Special healing : you can heal any wound and save the person no matter the condition they are in .

Killer touch : once you touch someone their energy gets sucked out and they get weak . If you touch them long enough and depending on the person , they may die. But it takes a long time . Not a quick attack . (If you want that to happen of course)

Shadows : having absolute control over your body , you create shadow like figures of it (like how perona makes ghosts bust similar to moriahs shadows .) .

This devil fruit is a logia type, attacks pass through you .. Your body turns into a black fog , known as fog of the death . that's how you can get wings and fly . Part of that black fog becomes hard like a bone and part of it covers it , Forming the wings . But you can fly of maximum 30 minutes

Why they call you a demon :
You are a human but since little age many people called you demon (not the revolutionaries) . Because of your strange rare logia fruit . Since you were young being called demon left a scar on your mind and you thought of yourself as a demon .
~☆~☆~☆~☆~☆~☆~☆~☆~☆~☆~☆
A/N
I will update soon and dont worry its just the beginning of the story . So you and luffy will get lots off time together and things will work out . Probably .
Zoro: I feel sorry that you love that rubber head .
Me:dont be mean zoro, just keep drinking .
And as I was saying , just be patient a little more . Im just getting started .
And what do you think of the devil fruit ? Should I change it or you like it ?
Author loves ya reader~chwan \(♡~\♡)