I was trying to one up a fellow writer.
Okay, so this writer I know (my sister and on again/off again beta reader) was writing a story loosely based off the characters of the Sander sides youtube videos (Deceit had just been introduced at the time). Anyways, she kept asking my input into her story and characters (stuff like is this in character for them etc.) and after a while, I got to thinking that I could probably do a better job with the characters. Not to say she was doing a bad job, I just thought I could do it better since I've been writing longer than her. Still, I didn't have a story to tell with them yet.
Then I was reading a fan comic (I think it was of MHA) where a character switched with an older version of themselves. It focused on the younger version in the future, but it got an idea stuck in my head. How weird would it be to come home to a complete stranger in your apartment, claiming to be your roommate from the future? And thus, the start of RomaMates was conceived.
I've gotten inspiration for individual parts from all kinds of places, but the initial idea came from those two things.