Despite her title, Maou is very easy to approach on a casual basis and much better than taking her off guard since she will be tied up easily if she considers it a learning experience. As nice as her bust is, however, she is very self-conscious about it and will remain passive so long as it doesn't receive all of the captor's attention. Focus on her hips, butt or spine instead. Use any kind of gag that brings out her hair and/or eyes and keep her squirming to keep her bouncing. After all, looking's for free.