By drinking from a vial of an ink-black bubbly liquid you've become a Magical Girl Nemesis.
*You can choose to stay on the world you are, living your own life, or choose to assume a different life and set of memories in a different universe, where people are generally more attractive, extravagant hair-color are naturally possible, and anime tropes are part of the rules of reality; basically a world perfect for a magical girl tv show. You can control the details of this new life, under the condition that it has to be fairly average.
*You have a one time free cosmetic change, allowing you to change your appearance, gender, and age. These changes with follow a logical sense: if you give yourself a perfect musculature, you will become as strong and agile as an athlete, if you give yourself a huge pair of boobs you will suffer from chronic back pain, etc...
*You are intrinsically connected to a brand new dimension of energy that you can access while sleeping or meditating. This dimension doesn't have many characteristics at first, but it does have a very unique feel to it and it appears rather ominous to the outside viewer, depending on your choices this ominous, corruptive feeling will become the main characteristic of your dimension.
*This dimension is entirely composed of a unique type of energy, which you can freely name. At first, it doesn't have a form or shape, but by your will alone it can acquire those things, becoming a vast extra-dimensional kingdom of your own design, complete with any retroactive history you decide.
*Inside this dimension, creatures named Denizens will form, either naturally or by your design, and they will fill any role you set for them and will adapt to any retroactive backstory you grant them.
*All Denizens are naturally loyal and subservient to you, with their personal opinion varied, but always loyal in their own way.
*The shape of your Denizens are highly adaptable, as their powers. Each of them have a 'power system' within themselves, which can take many forms. It can be a magical system, or an evolutive mutations, or technological knowledge, or psionic potential, or every combinations of those. All that matters are that your Denizens have unique powers that can evolve and they can acquire new ones with time and experience.
*You can directly influence their power system, and you have an instinctual understanding about the balance that must exist between the immediate strength of a Denizen and potential strength of it. You can also sacrifice one thing for another, making a titanic song denizen who lost the ability of becoming stronger, or a weak denizen who have potential to become godlike. You can also leave a Denizen with a shapeless power system that will naturally reform into something else.
*Your presence in the world will slowly allow your dimension to inject its unique energy in it, slowly eroding the boundaries between the worlds; this is a process that will take some time to finish.
*As the boundaries of the dimension grows thinner, the denizens of your dimension will start to slide in or actively invade the world you are in. Their actions are fully depended on their nature, desires and personality, but it's almost guarantee that they'll cause some kind of incident. You do not know when or where your denizen will appear, nor do you have direct control of them when they are loose upon the world, unless they are in your direct presence, as they can't or have any desire to disobey your orders.
*The otherworldly energy can also infect the population of the world, slowly or quickly corrupting them and turning them into new Denizens. This effect can also be achieved by the actions of the invading Denizens themselves if they have the means to corrupt someone.
*The otherworldly energy will cling around any denizens present in the world, slightly distorting reality around them. Normally, the denizens don't have the power to influence this, and the distortion will come in the form of a cloak of invisibility that affects the denizen and the wider effect of their actions. You can change that according to your will; making so the denizens are able to influence the cloak, making so the cloak take the form of a localized pocket dimension related to the denizen powers, making your denizen and their actions visible to all.
*You have the power to create a special type of Denizen named General, a General is a Denizen with great power and potential who can naturally command other denizens, they are natural rulers and monarchs, always having positions of great power and influence within your dimension. As with the denizens, their forms, personalities, powers and potential are up to you to shape.
*Generals, unlike your denizen, have a 'final form'. This power temporarily changes the general's shape to a different one, usually making them look more demonic but it can be anything, and greatly increases all of the General's attributes while spontaneously granting them new powers and abilities. This power can only be used in times of great need, great emotional turmoil, or with direct order from you. Only an experienced General who trained specifically for it may use that form at will.
*Your Generals can only enter the world properly when the boundary between worlds are close to the breaking point, so they have to find other means to affect the world indirectly. There are two common methods that every General can use; one is the 'Avatar Method' in it the General creates a proxy body identical to their normal one inside the invaded dimension, with it they can freely interact and play around in the new dimension, though their powers are stay very limited in that state. The other is the 'Possession Method' where the General possess the Denizen or a local individual inside the invaded dimension and acts through them, the relationship between the General and the one they are possessing is unique to them, and the power a General can push through depends on the resilience of the host they chose. There are other methods available, but they highly dependable on the kind of unique power a General can have.
The more Denizens appear, and the more the Generals act upon the world, the greater the pouring of energy from your personal dimension to the world becomes. And the more energy of your personal dimension is within the world, the stronger and more powerful you get. You can influence your own power like you would a Denizen, creating one or multiple power system for yourself, with infinite potential for growth. The thinner the boundaries between world gets, the more flexible you can make them.
*Once the boundary between worlds breaks, your personal dimension will fuse with the one you currently are, and you will become a utterly omnipotent god while inside it.
*Your dimension needs sustenance to exist however, and it gains sustenance by consuming other dimensions. So eventually you'll have to use your omnipotent power to fling yourself to another dimension, usurping another life with a free cosmetic change and starting all over again.
*On this 'fresh start' you may wipe away the accumulated characteristics your dimension acquired, truly starting from the start. You can also spare individual General or Denizens if you wish, or make them reincarnate with the memories of their previous incarnation. You can also decide to keep your personal dimension exactly the same.
*No matter where you are, what you do, or how much you try, your presence in a world will always stimulate it to form a magical girl system to fight against your invasion, or if the world already have one,it will make the girl of this system turn their attention towards you.
*Beware because if a girl succeeds too much in killing your Denizens and Generals, purifying too much of the energy of your dimension, or if they manage to find and kills you, it will overthrow off the hold your personal dimension have upon their world, and it will take some time for you to reform and try again on their, or another world. If this happens while your dimension is critically in need of sustenance, you and your dimension may actually die.
*It is possible to corrupt a Magical Girls and turn them into Denizens, these special Denizens are named Divas and they are unique because they will maintain a corrupted version of the powers they have as a 'regular' Magical Girl, a combination that usually gives then initial power and a potential greater than even the Generals.