Tamaki was scared.
He was almost always scared, or at least uneasy. He had been wary of the world and its judgments since he had been born, and still hadn't managed to cast off the mental prison he cast onto himself. Mirio had changed his life by being such a good friend to him, for making him realize he had to push through the anxious feelings he had and just... do what he to be done.
There was no turning back.
He didn't know what happened, since it had happened so quickly. You were fighting a difficult villain, one who was an unfortunate match for your quirk; the villain had easily tossed you to the ground like a piece of trash and Tamaki had watched in horror as your injured body finally stopped rolling against the concrete. He felt like he was shaking, and even if he wasn't, he knew that he was terrified.
Terrified for you. For himself. For the fate of the city.
He clenches his fists and tries to think, tries to remember everything that had brought him up to this moment. All the training he had gone through, all of your encouraging words to him, the complete faith that everyone showed in his ability...
He dives in front of your body and shields you from the next attack that would have no doubt cost you your life. He can feel that familiar feeling burning in his heart, the one he felt when he realized what had to be done. He stands tall, thinking of his next move to take on the villain who had hurt you so gravely.
"I'll protect you no matter what... Even if it kills me..." He whispers under his breath. "It's my duty... as a hero!"