Bugged or I made a mistake?

[JahGanu]

Hi all. I finished doing all NPC quest for true ending,but after I defeated Aether,I picked the 'Accept the offer' option first. Now,after I respawn at the branch, Aether doesnt spawn. So should I pick 'Decline the offer' first? Does this order of picking choices really affect the game?

[Nhat]

Well it ends the game.
I see a lot of people talking about savefiles, so I assume you need to change around those to get back before you got thw achievement and pick the other option.
That or play as intended and beat the game 3 times and get all endings like that.

[WildCard65 the Waifu Card]

There are 3 endings, 2 of them are tied to the part involving the offer to join them.