bh6fanatic:

The quote is from one of Disney’s bedtime story books. The one for BH6 was bittersweet. Basically, Hiro won’t sleep because he’s trying to invent a machine to put out fires. The reason he’s doing this is because he doesn’t want anyone else to get hurt in a fire like Tadashi did

xenomorphity:

Okay theory time! I think this will become a habit of mine lol but anyways!
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I think there’s so much more to these scenes than most of people think. If you watch Hiro closely in the beginning of this movie (when Tadashi was still alive) you can see he’s clearly hiding his true emotions under that cocky ego. I think Hiro was very depressed and insecure about himself to begin with.
What if Hiro had always been depressed and Tadashi knew that?
Maybe that’s why he always was so gentle and cheering to Hiro? And worried. You remember the scene where Hiro left Tadashi hanging by not returning the fistbump?
If you saw Hiro’s face, he was so anxious and insecure. He was already sad because he thought he can’t do it. And immediately Tadashi got worried, his face went a bit upset and he asked Hiro if he was okay. And Tadashi wanted to share everything positive with Hiro.

So, when Hiro was acting out (being a teenage criminal) what if he was just trying to cover up all his sadness? Maybe getting his busy brother’s attention? And Tadashi was the only one in the world who could cheer Hiro up. And when he said “I’m not giving up on you” Tadashi meant he won’t give up until Hiro would get better.
So when Tadashi died, nothing mattered anymore, he didn’t have a reason to act like everything was okay.

Conclusion: Hiro was already deeply depressed before Tadashi’s death.