You really have to hand it to Aizen — he’s never disappointed in the outcomes of his schemes. There’s never “it didn’t go as planned” for him, only “even better than I planned”. Even while Tousen is ragging on Masaki’s interference in their tests, Aizen finds everything to be just marvelous. They mention something about the hollow’s “final form” which I’m guessing refers to the one-time-use explosion that Isshin saved Masaki from at the end of the battle. It might have something to do with Ichigo’s second level hollow form or his final bankai. Potential relations are still very vague though, so we’ll just have to wait and observe along with Aizen to see what happens.
Things along Isshin’s side are getting interesting as well. He is shocked to actually meet a living Quincy, and Masaki is just as surprised by his amiable reaction. If she thinks all the shinigami are like Isshin though, she’s in for a nasty reality check. Despite her naivety, I definitely see some strong chemistry between them already, and even Ryuuken and Katagiri back off without revealing themselves despite the fact that Isshin is a shinigami. Unfortunately they end up parting ways without really introducing themselves. Masaki ends up keeping him on her mind (instead of her hot, and slightly nerdy cousin who her classmates seem to be into) even though she doesn’t even know his name. Of course now that Urahara is getting involved, that may change.