This app was mentioned in 1 comment, with an average of 4.00 upvotes
There's an upcoming mysery game called Antioch that you might like. There's also a game called Lovestruck in New York but the writing isn't that great tbh. Oh, and there's A Normal Lost Phone but the game itself is just for PC. And there's a game called Ice Void but it's Apple only.
I think Mystic Messenger is pretty unique as an otome game, though. However, given how popular MM has been, I imagine some otome games may try to follow in their footsteps at some point. And there's always the possibility that Cheritz might do a similar game, or add more content to MM (crossing my fingers for the latter, personally).