The Forgotten City

This can be easily achieved on a repeat playthrough by choosing the Soldier option at the beginning. Once you get to the city, run to Sentius and shoot him with your gun.

Easier than it sounds. Make a new game and select the soldier option when talking to Karen. then once you get into the forgotten city (past) shoot galerius and wait for sentius approach the stairs and shoot him too. here is a video for reference:

If you are interested in a full walkthrough with all achievements check the video below:


Timestamps:

00:00 Intro
01:43 Day1-Ending1: Tourist, Maverick, Law Abiding Citizen, The Many Shall Suffer Achievements
03:05 Day1: High Diver, Smooth Talker, Callous, Lopper Achievements
12:42 Day2: Medic, Counsellor, Trickster, Match-maker, Fibber, Bloodless Shadow Achievements
22:02 Day2: Allergic, Golden Archer, Striker, Survivor, Lion Tamer Achievements
29:43 Day2- Ending2: Treasure Hunter, Italian Plumber, Dead Shot, The One That Got Away Achievements
33:45 Day2: Grave Robber Achievement
35:16 Day3-Ending3: The Ones that got away Achievement
36:40 Day3: Archaeologist, Sleuth, Nimble, Liberator Achievements
43:17 Day4: Avid Reader, Unhygenic, Underworld Explorer Achievements
46:50 Day4-Ending4: Herculean, Silver Tongue, Minimalist, The Oracle, The Canon ending Achievements
51:44 Psycho Achievement
54:14 Kleptomaniac, Super Looper Achievements