While Ty contemplated how to corrupt the world he over heard some J-Pop song he knew from an anime coming from someone phone, probably their ring tone. Hearing this gave Ty a unique idea 'I'll corrupt the world with magical girls.' he thought, 'Of course not just magical "girls" no, no, no.' he added as he started thinking in detail how he wanted to do this.
First of course were the magical girls, or more accurately Magical Futa, yes futa. Ty had a big futa fetish, and honestly believed that if everyone were futa it would fix a lot of problems, but how and where do these soon to be futa's power's come from? Taking inspiration from one of the more popular, if darker, takes on magical girls, Ty decided that every magical girl will have gained the powers from one of Ty's representatives. This representative will grant the wishes of boys, and girls, and once they do that boy or girl will gain the power to become a magical boys and girls, gradually becoming futa as time goes on. These wishes will decide their power, and the costume, with wishes such as to be a doctor resulting in a medical looking transformation with healing powers, and being a super hero resulting in some specified power and a generic super hero transformation with a magical boy/girl flare.
These wishes and transformations will start our innocent enough, but over time the magical girl will be corrupted, as their wish becomes a fetish. The wish to become a vet will turn into a beastiality and furry fetish, the wish to be free will become a fetish for exhibition so on and so forth. Any fetishes they already had (if they did have them) will manifest as new powers, and/or new transformations, and any wish which would manifest as a fetish Ty doesn't like will slowly alter in a way to become one of Ty's biggest fetishes. This corruption will not seem strange to the magical girls, or to anyone around them, even if they notice it they shall simply perceive it as their powers growing.
The magical girl's will fight against Monsters, manifestations of humanities sins, such as hatred, pride, envy etc. When these monster's are defeated they area they were in will see a decrease of that sin, but it shall also have an influx of the magical girls's magic. This will corrupt the people of the world as the inhibitions decrease, and they become less ashamed by their fetishes, even more so if they have the same fetish as the magical girls. Over time the corruption shall also change women and girls as they grow cocks and their breasts grow bigger, even spreading from humans to animals as gradually the worlds only gender becomes futa. No one will ever notice this and eventually they will think this is how its always bee.
As the girls fight more and more Monsters the sins of the world decrease, and after a certain point one of the worlds greatest sins will become manifested as more powerful Monsters, Monsters representing the sin of Chasity. Once the magical girl's begin fighting against these Monsters the world will become more and more perverse and depraved. People will begin to go out naked, unashamed, they will have sex in public, and they will have no shame about their fetishes. This also marks the point when all people gain the capacity to enjoy all fetishes even if it isn't their favorite, the ability to enjoy all of Ty's favorite fetishes, and this is the point that people become more and more beautiful. The magical futas will believe the reason for this is because the world is filled with less sin.
Once the corruption of the world is complete, and it has become the perfect paradise of futa depravity, the magical futas will stop fighting monster born of human sin, for there is no human sin left. Instead the magical futas will become celebrities wanked off to by the masses, occasionally fighting monster's created by other magical futas not out of need but for excitement and entertaining others. Other people can become magical futa's with ease, by simply going to one of Ty's representatives, filling the world with yet more lust. It will be a fetish paradise where fucking is normal, and magic is everywhere.
Ty created his representatives, a hundred for every city unable to be seen by any they do not wish to be seen by, and sent them out to create his magical girls. Now who became the first Magical Girl