Finally, plot is important. Have a clear story arc that involves the yuri relationship as a central part. It could be a story about the OC and her love interest trying to overcome a threat in the magical world together. This not only adds excitement but also gives the relationship a context to grow. Also, don't be afraid to add your own unique twists. Maybe your OC has a special power that affects the relationship in an unexpected way. Just make sure it all fits within the framework of Madoka Magica.