At the beginning of the anime, after Mahiro gets eaten by Homunculus Mita. In the manga, Mita then eats Kazuki as well, only for said Hero to summon his lance and burst out, killing the snake from the inside. In the anime, Tokiko arrives before that can happen, summons her Valkyrie Skirt, and while hardly moving her own body, calmly and efficiently hacks him into pieces, almost literally dismantling Mita. Kazuki still gets his Big Damn Heroes moment later in the episode, though.
The revelation that Captain Bravo's Buso Renkin is purely defensive. Meaning that all those rapid fire punches that can break through rock and punch holes in enemies is all under his own power.
Near the end of the series, when he's faced with the choice of saving the world, or himself, Kazuki asks: "I'm going to protect everybody, but who's going to protect me?" Just before the Alchemist Army rescues Kazuki and Victor from space, there is a Call Back to that line. Then Bravo tells Tokiko to go and use his Silver Skin to help Kazuki make it to the flying robot (it makes sense in context), and gives the line "It's YOUR job to get him". We get our answer. And it is awesome.