Not all of these choices may matter (i.e. some battle choices), but these are the decisions I made in-game to get the ending for this trophy.
*** Spoiler - click to reveal ***Prologue
(What should I do??) - Use knife
Chapter (Quest) 1 – Part 1
(But…) - Use knife.
Chapter (Quest) 1 – Part 2
(I see both points…) – Hey, don’t attack Hiroya.
Chapter (Quest) 2
“That might be true, but… - We don’t have to rush
(I’m scared… But I’m not alone. Hiroya and Libera are by my side!- Use knife.
(It only has a little HP left…) – Play harp.
(That’s not true. Why is he like that?) – You’re already helping me a lot.
Chapter (Quest) 3
“I…” – I want us to work together, Hiroya.
(I need to fight, too.) – Use knife.
(Hiroya is asking so desperately…) – I need to ask Radius too.
Chapter (Quest) 4
(Is it something difficult to bring up?) – “If it’s not a big deal, then tell me.”
(He’s still hung up over being tricked by Libera…) – I think we can be honest.
Chapter (Quest) 5
(I didn’t know Hiroya felt that way.) – You’re making me blush
(I may just cause trouble for everyone, I know that…) – I really want to go with you guys.
(I gotta fight, too!) – Play harp.
Chapter (Quest) 6
“Don’t be like that!” – Hiroya didn’t do anything wrong!
Chapter (Quest) 7
(True. Since most of us are Demons, we’d need to have a Demon leader.) – I think you should do it, Hiroya.
(I think…) – I don’t want to be separated from you either.
After you make the last decision, the end of the game will play out, the credits will roll, you'll view a few after-credits scenes, and the trophy will pop.