Anger, pain, and betrayal hit him all at once and in his state of despair the urge to gain revenge for his brother's death in vain takes over Hiro. Tadashi died for nothing. Hiro should have stopped him when he could, should have held him back or ran after him - better the two of them gone than Hiro left behind with a gaping hole in his heart in the shape of his older brother.
Guilt and anger bubble up within in and he feels as if he's being suffocated by the two emotions - he has to physically breathe through his nose and a burning pain begins within his skull.
"Baymax, destroy him!"
Hiro sees Callaghan's terrified expression and pride surges through his veins. He wants to see Callaghan suffer and die a painful death just like Tadashi had.
Everything flies by so fast and the next thing he knows, Hiro is staring at his older brother's tired face... smiling face... proud.
Tadashi wouldn't have wanted him to take revenge. His brother's dream was to help people, he loved life and if he knew that Hiro would take a life without a second thought, command Baymax, his invention to help people, to kill... he would be so disappointed. So upset.
But if Tadashi were here, Hiro wouldn't be in his state of mind, so crazy and devastated.
Hiro wipes away his tears. "Tadashi wouldn't have wanted this."
He thinks he can almost feel his older brother ruffle his hair in approval and it takes all of his strength not to cry once again.
"Miss you."