Alright, if you want you can always learn more about what I'm saying, or more detailed than what I deem necessary, about Arturo and the game plot at Bleach wiki.
Arturo was really the first of the first Arrancar, a true natural Espada of sorts. He was however, only as strong as the average Numeros and such. His zanpakuto is what made a difference. His zanpakuto was named Fenix, and held only one, truly terrifying power. When released, if Fenix delivered a fatal blow to the opponent, one that would end the battle, it absorbed all of the defeated foe's reishi and added it to Arturo's own. Because of this, he could gain endless power and make sure none stood stronger than he. After defeating half of the Gotei 13 with little effort and time, Yamamoto ended the fight by sealing him beneath the Sokyoku in a special chamber. When the Sokyoku was shattered by Ichigo, Arturo escaped and began stealing power once more only to be put down or sealed away for good.
The main things about Arturo (that we can apply to whatever villain takes the stand) are the following:
His Reiatsu: It was so great it was truly terrifying and in one game even caught Aizen's attention. It emitted from Arturo's body in the shape of wings (which caught fire in his release).
The ability to shape shift: Needless to say the greatest villain's weapon is trust and this is how Arturo obtained it, able to shift into people or zanpakuto spirits.
His Zanpakuto: As the series has shown so far, the main villains have very unusual weapons (the bakoto, Aizen's zanpakuto, the full bring). Arturo's was no different, allowing him to obtain the reiatsu of his foes and wield it as his own (for a good example I refer you to the Samehada from Naruto).
I think those are the main things about the villain, if we take that course of action. If we decide to take the rebel story, then I can work on that from there since I have it built already for the most part, it just hasn't been put into action.
