I <33 this scene. So much is going on.
That look Heero gives her at first. He really is a kind person and he does not want to kill this innocent 15 year old girl whose only crime was that she was at the wrong place at the wrong time. Well, that and being too curious for her own good. For just a second, he shows what’s really on his mind: he regrets this and it will destroy yet another part of his kindness. But, again, don’t ever think that’ll stop him.
Relena sees this look, but misinterprets it as “reaching” him. This is, what, the third time she’s made this mistake? It’s not surprising, given her forgiving nature, but seriously, girl. Have some self-preservation instincts already. That is why, when Heero actually pulls the gun on her, she is so stunned. I don’t quite think this turned out like she thought it would. Then again, as Heero says, (in the English one, at least), she is “in over [her] head.” It’s sink or swim in this war, and we’re going to find out whether Relena, having dived in head-first, will drown.