*Spoilers Ahead* First paragraph minor spoilers. Code descriptions contain major spoiler's that should not be read until one full playthrough.
So to get this achievement you have to play through the game at least two times. The best way would be to do the good end (Dweller in the Dark) and the bad end (Heirs). The reason why is you get a blood code for reviving a successor and a blood code for killing them. To save a successor you have to find all their memories before the boss fight. Watch all the cutscene's at the attendant to make sure you have them all. Once you beat the boss and they're a stone statue, click on them and you should be able to restore there memory. To kill them once you get to where they are a stone statue just walk out the door without reviving them. The NPC's will all give you their blood codes throughout the game as well. So when you beat a boss talk to them at home base and you will slowly collect their codes. The further down the list the farther you will be in your playthrough before they give you their code.
They're 32 blood codes total. I will list the codes in order from top left to bottom right with descriptions of how to get them. All codes will be in this order regardless of when you get them. Almost all of these you will get easily with two blind runs of a good and bad end. If you have 31 codes and your missing one it's probably Demeter. This is the most obscure code in the game and is the second from the bottom.
Queenslayer: Received once you complete the map Memories of Player and beat the boss.
Fighter: Starting Code
Ranger: Starting Code
Caster: Starting Code
Berserker: Story when you beat the first boss Oliver
Prometheus: Louis will give you this blood code. Talk to him at home base regularly.
Hunter: Found on the Ruined City Center Map. Once you see the cutscene about human blood. Go down the ladder and follow the path. You will see a group of five lost patrolling. Take a right and you will be invaded. Look around this area and it will be on the ground glowing red.
Mercury: Coco will give you this blood code. Talk to her at home base regularly.
Hermes: Davis will give you this blood code. Talk to him at home base regularly.
Darkseeker: Pick up off the ground after beating Insatiable Despot in the Dried-up Trenches
Atlas: Yakumo will give you this blood code. Talk to him at home base regularly
Assassin: This is a pick up in the Howling Pit. The easiest way to get to here is teleport to the first entrance mistle. Go down and huge the left wall all the way across the map. There will be two enemies you will have to fight. When hugging the wall take the first left (it's a long run). Then go straight you will see an enclosure with a Elite Lost (Big dude). Kill him and it will be up the ramp.
Artemis: Mia will give you this blood code. Talk to her at home base regularly
Isis: Beat the Successor of the Ribcage. Save Aurora instead of killing her.
Queen's Ribcage: Beat the Successor of the Ribcage. Kill Aurora instead of saving her.
Eos: IO will give you this blood code. Talk to her at home base regularly.
Fionn: Beat the Successor of the Breath. Save Nicola instead of killing him.
Queen's Breath: Beat the Successor of the Breath. Kill Nicola instead of saving him.
Survivor: Found in the Ashen Caverns right before the boss room. Going to the boss it will be on the right split before going left into the boss room.
Dark Knight: Defeat Gilded Hunter
Scathach: Beat the Successor of the Claw. Save Emily instead of killing her.
Queen's Claw: Beat the Successor of the Claw. Kill Emily instead of saving her.
Harmonia: Beat the Successor of the Throat. Save EVA instead of killing her.
Queen's Throat: Beat the Successor of the Throat. Kill EVA instead of saving her.
Heimdall: Jack will give you this blood code. Talk to him at home base regularly.
Hephaestus: Rin will give you this blood code. Talk to her at home base regularly.
Warrior: Found in Crypt Spire. Teleport to the first Mistle. Play the level as normal. You will get to a point where the path splits and you will go right. The room your looking for is the room with the Big lost and the four monkey lost, there will also be a lever in this room. Instead of going straight throught the room turn right and go up the ladder. It will be in the middle of this platform.
Scout: Found in the Rocky Ruins Depths Map. The map is given by Richard after doing the Self-Important Revenant side quest. It will be down the right path facing the way you teleport into the Depths map.
Queen: Beat final boss on the good ending.
Hades: Defeat the final boss on either playthrough
Demeter: Easily missed. Once you beat the four successor's on any playthrough teleport to the Cathedral crypt of ribcage location. You will want to visit Karen which is down the steps and in the blood bead room. It will be sitting in front of her.
Ishtar: Defeat the Queen's Knight Reborn.
I hope this helps. If it did feel free to give a thumbs up :). If downvote please let me know what I can fix to make the solution better.