It was one author after another, in series instead of parallel. The first author was unable to continue, and so the editors arranged to have me step in, and the original one approved it. The entire outline and the first eight chapters were complete, but there were a lot of loose ends because of the combinatorial complexity of the last few chapters (you can pick from a lot of different clubs, each club can have different plans, you can be working with others or not, etc. and the endings can change a lot depending on who you befriend and romance). So I finished those chapters, then went back and expanded on the early chapters in response to reader feedback to add more variety, paths, background info, location detail, conversations, etc. Because the first author had stepped back from writing, I just focused on keeping the whole thing coherent, following the outline, and reading a lot of background material (including purchasing the Sailor Moon Eternal Editions, which are great).
I liked the whole thing quite a bit. I’ve always been more productive at editing pre-written material and writing branches and filling in than at coming up with new material (I can double my writing pace when there’s already a skeleton in place), so I definitely could see myself collaborating like this in the future again. But I’ll have to see how people feel about this game first; while I didn’t write the first few chapters, I did revise them over and over and get lots of player feedback and did everything I could, so this represents my best work. If people like it, I’ll definitely be interested in more collaborations, but if not, I’ll have to dig in and see what went wrong before I try something like this again!
On a side note, being both an author and a collaborator puts me in the strange position of being a fan of the game, even though my name’s on it. I really got into the characters, and drew some fanart of them: Unofficial character art for Star Crystal Warriors Go
Here’s one example from that thread (your animal companion, Polaris):
These portraits wouldn’t work as character portraits because all of the characters can flip genders (and, in Polaris’s case, species), but it was fun putting my imagination out there. I head-canon all the main characters as women (in the tradition of most Sailor Moon characters and Madoka Magica) but included male and non-binary references for the art to help visualize different genders for characters when working on the end chapters. Kit’s my favorite romanceable character (a nemesis with a taste for drama), with Morgan (your childhood best friend and neighbor) second. The first author created them, and they’re a big reason I worked hard to finish the game, to give them a good ending (to tie this post back to your original question).