Sequence 9 has a a total of 4 memories.
You will unlock this achievement after completing all 9 sequences (follow my other guides for the list of other sequences).
For this ending, you do not have to kill the extra 4 E Citizens (the other 2 occur through natural progression of the game).
I wrote this guide as a simple checklist (click on the spoiler if you do not mind seeing the title or “subtitle” of the memory) to help you keep up with: what you have completed, how many memories you have left in the sequence, which memories have secondary objectives, and what those objectives are (so you can prepare before starting the next memory).
*** Spoiler - click to reveal ***
Sequence 9
Memory 1: Abandoning Pretense, “Unmask the truth”
Memory 2: Confronting Agate, “Confront the mentor”
2ndary Objective: Complete the mission in 5 minutes
2ndary Objective: Take no damage
Memory 3: Reconciliation, “Repent and join the order”
2ndary Objective: Kill the Citizen E in less than 2 minutes
Memory 4: Erudito, “The Truth”
2ndary Objective: Don’t take any damage
To keep this solution clean and concise, I have not included hints for the secondary objectives. I wrote this to help in planning ahead (getting enough poison darts, bullets, or smoke bombs) to make the second objectives easier. Please comment if you do need any help and I will provide any help or suggestions I can. I hope you find this helpful and good luck going for 100% sync!