Naturally, one of the first things that come to some people's minds when they see OC x Canon is.... "OMG U HAVE A MARY SUE." I can't begin to explain how much this irks me! It's very ignorant to judge a character solely on their relationships with canon characters without looking at the character as a whole. Now if the character is gorgeous, without a flaw in personality, the most powerful Shinigami/Espada/Quincy hybrid of nobility and with a tragic past that was related to different canon characters and had three canon characters in love with him/her, THEN it would be all right to label this character as poorly developed. (No, not Mary Sue/Gary Stu, I really dislike this phrase that people throw around so carelessly without fully understanding its meaning.) I feel that OCs really do add some variety and spice to any fandom! And it's quite interesting to see when one is paired with a canon character, to see how the relationship is different from the obvious canon pairing in the series. It's okay for some to believe that another character could work better with Aizen then Momo, Orihime, or another canon character. (Though I personally wouldn't pair an OC with him, only because I feel he's rather bland.) :P Yes, you could argue I'm only defending this because I have an OC x Canon pairing of my own, but even before I created Mari I've always loved them. We can't help our fangirl/fanboy tendencies to create an OC for our favorite Bleach character, though I would stay away from making your OC a self-insert. Make it an exciting OC by making its own character, not based off yourself! (It's not like all the Bleach characters are copies of Tite Kubo.)