>>542171514
I'll give you a real answer just in case you are serious.

Short: Whatever you want. It doesn't matter unless you have a certain desire for what you want to create. SMT has a text only fan game and that one is great to play for example.

Long: It depends on what you desire. If it's 2D, then you can use any version of RPG maker or Renpi easily. RPG maker gives most upfront content for RPGs, where for persona summoning it would have to be done with UI and animations. If 3D then you would want to use a Japanese engine like Bakin or use Unreal. Niche engines offer less control but usually solves some sort of issue with Unreal where the trade offs may become worth it to use depending on what you wan to focus on. Unreal offers the most freedom and control over the graphics, but isn't simple compared to 2D. It also has the asset store which makes it very easy to download random ass models/code to create an environment that fries your GPU. It also has a free to download RPG toolkit, but anything more technical will be a strain to edit to work with it. E33 uses the free tool kit and it's able to do it's own thing due to drastically reshaping it. Unity has become a meme as of late, especially after it was revealed for 8+ years there was an exploit in a single file that would allow remote execution. (https://unity.com/security/sept-2025-01/remediation). Do a bunch of research before starting for the ideas you want and the ideas you can actually do reasonably.

Since you are asking /pg/ instead of any other place on /vg/ and/or /v/ for this, I would say use RPG maker. You can make a prototype quickly along with the free content in engine and online being enough to make something without much effort. A majority of porn creator's fan games use RPG maker and they have calendar systems since it can be done with a single plugin that is plug and play.