It’s best to save this achievement for the very end, once you’ve completed the main storyline and unlocked all other achievements.

Fully charge the Assassin's Focus gauge, then head to the Damascus Gate and configure your equipment as follows:

• Equip the Initiate of Alamut Sword (starter sword).
  
• Equip the Initiate of Alamut Dagger (starter dagger).
  
• Equip the Initiate of Alamut Outfit (starter armor and attire).
  
• Do not equip any talismans.
  
• Do not apply any dyes.

I had my weapons at their base levels, while the armor was upgraded to level 3. Upgrades shouldn’t affect this achievement, but it’s good to keep these details in mind.

This step is optional, but I’ve seen these tips mentioned in various comments and followed them as well:

• After configuring your equipment as outlined in step one, create a manual save in a new save slot - do not overwrite your current save (if you don’t have free slots, you can delete one by right-clicking on it).
  
• Once saved, exit the game and restart your computer (the goal is to close all Ubisoft-related processes and applications).
  
• Relaunch the game and manually load your save (do not use the "Continue" option).

It’s important that during the entire process described below, you do not load/save the game or use fast travel.

When you’re at the Damascus Gate, approach a group of merchants and hire their services. Walk through the gate, and as soon as you have five guards within range, perform an assassination using Assassin's Focus (default key: R).



Next, move to the Prince's Palace location. On the way, make sure to charge the Assassin's Focus gauge. Once you’re at the location, pay the merchants again, enter the area, and when you have five guards within range, perform an assassination using Assassin's Focus (default key: R).


After completing these steps, the achievement should be unlocked.

I hope this guide helps you unlock the "Blade in the Crowd" achievement without any issues. If you still encounter problems or have questions, feel free to share your experience - I’ll do my best to assist further.

A big thank you to everyone who contributed tips and solutions, especially Lee from the Steam discussion thread, whose insights were invaluable in cracking this tricky achievement.

Good luck, and happy gaming!