Tahu: No. No, I am not well. But... I am alive, and in your debt, my sister.
Keep in mind that they've spent the rest of the movie and half of the events before it bickering with one another.
The thing that really got This Troper in that scene was how small and fragile Gali's hand looked in comparision to Tahu's.
Turaga Lhikan's Heroic Sacrifice, and his last words to Vakama in Legends of Metru Nui. It's especially powerful when one remembers that Vakama had spent most of the movie doubting his ability to be a leader, questioning his visions, and blaming himself for Lhikan's capture.
Vakama: That was meant for me.
Turaga Lhikan: No. This is my lifetime's journey. Yours lies beyond. Trust your visions. I am proud to have called you "brother"...Toa Vakama.
The scene at the end of BIONICLE 2: Legends of Metru Nui where Vakama gives Turaga Lhikan's mask to Jaller, whose Matoran mask is broken, and then it molds to fit his face, is incredibly Heartwarming.
This makes Jaller's Heroic Sacrifice in The Movie when Takua is under attack by Rahkshi Turahk even more Heartwarming, because it means that some of Lhikan's spirit lives on in him, and so means that the already Heartwarming moment when the Takanuva-Makuta hybrid being resurrections him from just the mask is just that much sweeter.
I liked it in "Web of Shadows" when Matau tried to reason with Vakama, how does he eventually snap him out of his Brain Washed And Crazy state? By jumping off a cliff knowing his brother would save him!
Vakama: (Matau manages to grab onto the edge to avoid plummeting to his doom.) You are weak, brother.
Matau: You're right, Vakama. I am weak... We all make mistakes, Vakama. That's what happens when you're brave enough to make decisions. I understand that now... (Vakama steps on his hand, trying to get force him to fall) Wait! I'm sorry. For doubting you. Our strength comes from our unity, Vakama. Which means... you can't be strong without us.
The ending of BIONICLE 3. Norik tells Vakama that the Matoran are now his responsiblity. Instead of reacting with crippling self doubt as he would have in Bionicle 2, he simply reacts with a "well how 'bout that?" smile to himself, neatly accenting the Character Development he's been through.
Matoro willingly gives his life to revive Mata Nui, and with his last bit of individual thought before transforming into pure life energy, teleports his endangered teammates back to Metru Nui and grants them the ability to breathe air again. This selfless act later causes the Ignika to commit a Heroic Sacrifice of its own because the mask was so moved by what Matoro did.