Haibane Renmei, character of your choice
Dialogue: "That's why they're like that."
"Who are the Toga?" Rakka asked one evening at dinner. "And why aren't they allowed to speak to anyone but the Communicator?"
Reki and Nemu traded glances across the table. Kana kept eating. Hikari looked around curiously, apparently wondering if any of the others knew.
Yuu gazed out the balcony doors thoughtfully. "The Toga bring things to the town from outside. I think they're some of the birds we see flying over the walls. They go around the town and see the things that we need. Then they go outside and bring them to us."
Kana snorted, despite her mouthful of food. "The crows are just crows. Scavengers."
Hikari scolded Kana with her teaspoon and grinned. "But they outsmart you every time, don't they?"
Kana stuck out her tongue at Hikari.
Reki said, "Well, if they're the birds, why would they bring things to the town, Yuu?"
Yuu shrugged and smiled absently. "I think they care for us. Maybe all the birds are beings that love us, and want us to... to not worry about things that mean very little. So we can do the things we need to do."
Nemu sipped her tea, then murmured, "Selflessness. Compassion."
Yuu nodded. "Compassion, that's the word." She turned a brilliant smile on Rakka. "So the Toga are the birds, and so they can't talk like us. That's why they're like that."
Rakka nodded solemnly, bowed slightly, and said, "Thank you, sempai!" which caused Yuu to burst into giggles.