Seriously, it came out of left field. And wasn't even developed until the peace dude started spouting the red string of fate BS to them. Akame, Leone, Hell even ESDEATH had more romantic development with Tatsumi more than Mine did.
Don't misundestand though; got nothing really against Mine. But I just don't think she was right for Tatsumi. So was kinda salty when they ended up canon in the Manga.