Azar (exclusive route for blood magi, reminder) has 2 ways to romance her (basically 2 different variables that directly oppose each other). When you first meet her she is somewhat insecure (which leads to a lot of stupid decisions on her part, you'll see in the next update). You can choose to either taker her seriously, which builds her self-confidence, which is the vanilla romance, or feed into her insecurities and treat her like a child, which is the "evil" romance. The diaper thing (and most of the more niche kinks with her in general) is only present in the evil romance, but it won't be optional with that route.
In general I've tried to have a different kink for each of the girls to give them more variety. One thing I found boring in Visual Novels in the past, while I was working as a reviewer, was when all routes led to the same basic stuff on the bed. I've put plenty of effort to have all the h-events be unique in BR. For Azar it's kissing and cowgirl for the vanilla route, diapers and spanking for the evil route. Each of the girls works with her own 2 basic kinks, more or less.