**MISSABLE**
At the start of the game after your second fight (where you get left in the room to die) you will speak to three samurai. After this cutscene plays turn around and walk back into the room you just left and then continue until you reach the small bridge you crossed in order to reach the first fight in the game.
At this point stand in the middle of the bridge facing towards the sunset and hold your "Soul Absorb" button for about 20 - 30 seconds and a save icon will appear in the bottom left and a flock of geese will fly across the screen and your achievement will pop.
Video guide below.
**Starts at 00:15**