The game is fairly simple, but still, here's a walkthrough! 

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Ending 4

• During the second choice, pick "Keep trying"

Ending 3

• During the second choice, pick "Let her die"
• During the third choice, pick "Stand on the track"

Ending 2

• During the second choice, pick "Let her die"
• During the third choice, pick "Shut her up"
• During the fourth choice, pick "Chase after Kai"

Ending 1

• During the second choice, pick "Let her die"
• During the third choice, pick "Shut her up"
• During the fourth choice, pick "Call out for Kai"