Cool. I have an idea for a ex-slave who was fed a Devil fruit while he was still in captivity. I have no idea what the fruit will do! Maybe something that has to deal with healing people, and sorta ripping them apart as well. Still an indea in progress.
A few ideas for character's. Let me know what sparks your interest.
A logia-user who has eaten the Kaze-Kaze fruit (Wind-Wind fruit). An ex-Marine Vice-Admiral who turned to piracy after Sakazuki ordered a ship carrying his wife and child destroyed during a hostage situation because he was unwilling to negotiate with pirates.
A swordsman who has eaten the Toki Toki no Mi (Time Time fruit) and has developed a unique swordstyle called Jikantoryu (Time-Sword style) around around "cutting" through time an altering the battlefield for himself and his foes.
A martial artist who has eaten the Oni-Oni no Mi: Model Shinigami (Devil-Devil Fruit: Model Reaper), an enormously powerful mythical zoan that grants him incredible powers over death, but comes at a terrible cost of eating away at the purity of his soul as a dark spirit whispers from within the depths of his mind.
Other fruits that could be interesting: Mizu-Mizu/Sui-Sui no Mi (Water-Water logia), Jo-Jo no Mi (Shape-Shape fruit) for morphing and disguise, as well as body alteration, Gen-Gen no Mi (Illusion-Illusion fruit), Tsu-Tsu no Mi (Pain-Pain fruit), Hitan-Hitan no Mi (Sorrow-Sorrow fruit) for the draining of joy and happiness, probably associated with cold and emptiness.