Only managed to get one ending regardless of dialogue options I picked, if there is more to it than that I'd appriciate some pointers.
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Hint 1: Hiro is mute, so ultimately dialogue matters very little. What's more important is what you do, rather than what is "said".
Hint 2: There are five endings total. Out of them, three are decided at the last few scenes, one can be done at any point after a certain time, and one has to be actively pursued through the game.