At the absolute minimum you need to have the ability to come up with a compelling story that people would want to read through. If you have no programming or art skills at your disposal, you can start with a simple text game using something like
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. Even if you want to create a game with graphics using a more suitable engine, Twine can be a great starting place to map out your story since it has a really nice flow chart style story editor that makes if very easy to keep track of your different routes and choices in a visual way.
If you want to make VNs then
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is usually just about the best framework to turn to. It requires really next to no programming to get up and running unless you want to add in game mechanics that are atypical of standard VNs, in which case you'd need to know a bit of Python and in particular how to work with
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, the underlying engine that Ren'Py is built on.
If you want graphics you have several options that will depend on your skill level and whether or not you plan to sell the game or not. If you don't plan to sell it and just want to give it away freely, then you can get away with a lot of stuff you wouldn't be able to otherwise, such as using stolen images from real porn or art grabbed from the web or even other games. This usually leads to poor results, and you obviously can't profit from it without serious risk, but it is the easiest way.
If you have any artistic ability in 2D or 3D then all the better, you'll want to leverage those skills. If not and you are at least willing to learn the basics of tweaking and posing pre-made models you can look into using
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or
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or
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to get pretty decent looking images with fairly minimal effort. If you want to be legit about it, then Daz will cost you a fair bit, since it is heavily focused around their asset market. The software itself is free, but all the assets you don't provide yourself or get from their free section will have a price tag associated with it.
If you don't have great art skills but would still like to learn and try your hand at making original work and you don't want to spend money on expensive software, then
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is a great free/open-source option for digital painting (though you'll definitely want a
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if you want to do digital drawing/painting). On the 3D side of things is
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, which again is free/open-source and an amazingly powerful tool that easily gives anything from Autodesk a run for their money.
It would also be a good idea to take a look through
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that's stickied here on this forum, it has links to tons of useful resources.