Re the promise. I've never read that so much as a promise or a vow, not like Tezuka's vow to take his team to Nationals. Because it's such a standard expression. That's what every team that loses to Seigaku tells them while Seigaku is playing anyone else, most notably in the Regionals matches against Rikkai. What it always boils down to is "I lost to you, now you're carrying my honor along with your own; if you lose, then I lose by proxy, so don't lose". When Ryouma tells Tezuka that, he reinforces the rival (or, at least, future rival) aspect of their relationship. It's highlighting the competitive part of their relationship, rather than the unified part (the team aspect that the Nationals vow calls on). And Tezuka accepts that and answers as he would to a competitor who said that.

That, to me, helps explain why Tezuka is challenging Atobe so brazenly to a long game, why he sticks it out to the utter, bitter end, and why he hasn't /actually/ lost in a very significant way. And why Ryouma, I would say, understands that Tezuka hasn't exactly lost. I think this is why Ryouma is so fired up, and why he's such an unspeakable little show-off in his game with Hiyoshi. Tezuka was challenging Ryouma, at the same time he was demonstrating what true loyalty to one's team means and looks like. Ryouma is answering Tezuka in kind.

Though I always wonder just how multi-purpose Tezuka's game, here, is--whether he's trying to galvanize Atobe at the same time as Ryouma. Tezuka seems to have some really strong tendencies to mentoring (even his trainer in Germany, for crying out loud); I wonder just how far they extend.