Phantasma did state in a prior 2025 Discord fireside chat that crossover events would be in the works if people wanted them, so it got me thinking on how we can pull it off. Now for all intensive purposes, let's say that ZUN has given his all clear along with the rights holders of the crossover IP in question, how do we make it work? I've got a few ideas, including on how we can really work this into the MV project colabs to make them feel more special.
First we need to figure out how to fit the characters in and how players can get them, for that, I suggest having the crossover character(s) paired with a Gensokyoan resident akin to Genic rares. How do we get them? well we'll need at least 3 characters to work with becuase the way I would have it is that upon clearing a crossover event story, on top of regular event clear rewards, you get a copy of that event character pairing for free. Would the characters be max limit broke out of the box? Let's be realistic and say no, which is why you would have farmable tokens akin to how we limit break/luck enhance Yukkuris. While the colab is going, there would be a special banner where you can use the tokens to get more copies of event characters to again, limit break/luck enhance. I'm gonna use an IP that frequently makes the gacha game rounds for an example of how this would work: Evangelion. Clearing the crossover story on normal would give you a free copy of Rei Ayanami paired with someone like Hata no Kokoro or Sakuya as a reward, hard mode would give you a copy of Mari Illustrious Makinami paired with Marisa and lunatic would give you a copy of Asuka Langley paired with Reimu.......or for lols, we could move Mari and Marisa into the crossover event token pool and for hard give players a copy of Shinji Ikari paired with Junko.
MV project crossovers would somewhat be similar, but since there's only one character at a time, we can just give a copy on lunatic.
Of course this is just a rough idea, feel free to add to it.