I find the other guides excessive and a bit too in-depth so here's my own take on Determiner of Fate.
Guide to Obtaining Determiner of Fate Achievement
In order to view all the endings and achieve Determiner of Fate, you will need 3 playthroughs minimum.
There is 3 different endings and I suggest clearing them in the following order:
- Neutral "To Eternity".
- Bad "Heirs".
- Good "Dwellers in the Dark".
The Good ending has an additional scene which you also need to watch in order to clear the achievement. That means, in the run for the Good ending, you will have to kill the final boss twice.
1st Run: Neutral Ending "To Eternity"
Play the game the way it was meant to be.
Make sure to restore at least one successor but not all of them. Consult guides for the Vestige placement if need be. You only need to save ONE successor.
2nd Run: Bad Ending "Heirs"
This is your speed run. The moment you spawn, send a distress signal. Rush. Run over all the mobs and don't take a single fight. You now know most of the maps well enough to know where you have to go. You will still get lost in Cathedral but it will be quicker then before.
Therefore equip Stamina passives. Bring your Ai partner. Most Coop randoms I got understood what I was doing, followed and helped me immensely. Both parties also receive Marks of Honor which helps with the Exalted achievement!
Rush to the end, save no successors at all and watch the credits roll.
3rd Run: Good Ending "Dweller in the Dark"
You have familiarized yourself with the game and now you truly know most of the stuff. Therefore rush through every map again. Send distress signals. Except for the ones where there are successors to save which are in the following order:
- Cathedral (Aurora - Isis Vestige).
- Ridge of Frozen Souls (Nicola - Fionn Vestige).
- City of Falling Flame (Scathach Vestige).
- Crown of Sand (Eva - Harmonia Vestige).
Consult guides! Use the maps to find all Vestiges immediately.
Make sure to restore the Vestiges before you trigger each boss fight. There is always an Io clone in front of each of these bosses!
After Final Boss! Determiner of Fate
You have cleared the final boss for the third time and achieved "Dweller in the Dark".
You have watched all the cut scenes, you are now in the home base and you cannot continue the game. When you have done all that you can do, when you have watched the final scene and credits roll, you are back in the Main Menu.
Hit Continue the Game
You are now back in front of the final boss. Unlock the Mistle, leave the room and go back to restore all EOS Vestiges. You can collect them now if you haven't before. Restore and repair them all.
Now clear the final boss once more.
Congratulations, you have now unlocked "Determiner of Fate".
- Each Successor has two different blood codes, one is given to you depending on whether you saved him/her or let them die. Practically you will unlock all hidden Blood codes by aiming for Determiner of Fate.
- The endings achievements really only regard the Vestiges mentioned above and disregard anything else.
- Your weapons, items and level carry over to the next game.
- You do not have to increase difficulty and I suggest you don't. You can do that afterwards too.
- All of my achievements unlocked before Determiner of Fate. I'm only missing Exalted which is a grind as you need 400 Marks of Honor in total.