BioShock Remastered

This one is actually incredibly simple and the better way to play the game.

So basically in the game there is a currency called Adam that is used to buy and upgrade your plasmids and tonics in the game. This currency is only gained from Little Sisters. With the exception of the first Little Sister you have to fight and kill a big daddy that is guarding the Little Sister. After this you are given the option to harvest or save the Little Sister. For the achievement you want to make sure you save every Little Sister you encounter, you DO NOT have to deal with every Little Sister in the game you just have save the ones you do. I recommend you save right before making the choice just incase you press the wrong button in which case you can reload and try again.

On the topic of Adam you get more upfront for harvesting the Little Sisters but every 3 you save you are given a gift of Adam which comes out to more.

Edit: A couple people are saying this achievement didn't pop for them at the end of the game so make sure you save right before the final fight and if it doesn't pop just run through the final fight again

Edit 2: Some people are saying it's specific to survivor difficulty some are saying it's not. I did have the game on survivor difficulty when I got it so try turning the game to survivor difficulty right before stabbing Atlas for the 4th time

Edit 3: basically the servers are sensitive so it doesn't seem difficulty specific but you may have to retry the final fight if it doesn't pop

This achievement requires that you do not harvest ANY little sisters on your play through. As long as you do not Harvest any little sisters, you will fulfil the requirements for this achievements. Thus, you technically do not have to do save every little sister in the game, just save every one you encounter. However, although "dealing" with all Little Sister's is not required, it is highly recommended that you do as there are only 21 and by saving all of them you will unlock this achievement and the "Dealt With All Little Sisters" achievement

Main bit: PLEASE make sure you have a good save right before the final boss fight (at the very, very end of Proving Grounds before you ascend the lift to start the final area)
This is because this achievement has an annoying bug with a very easy fix; for some reason, I can confirm this will not pop unless the game is finished on the new hardest difficulty "Survivor", or at least this seems to be continuous with everyone I know who has gotten this achievement (why this happens I do not know.) Thus, you might unlock this when you should as it should unlock when you try for another difficulty related achievement anyway, so this isn't the end of the world.

To get "Brass Balls", you will be doing a trick where you play the entire game on easy and when you........ and switch to hard by pausing........ Do exactly this for Brass Balls, then reload your save and do the same except switch to survivor instead. This popped it for me and everyone I know first time, and is required anyway to get "Seriously Good At This", so you very well might not need this at all!

Thought I'd do the solution as there seems to be some confusion. To summarise, do the difficulty glitch where you switch difficulty.

For anyone interested, use the electric gel in the chemical thrower. Downs the boss 3 times in about 45 seconds (literally)

Cuidado pra não perder essa conquista,sempre faça um save manual.

Após lutar com o Big Daddy,salve todas Little Sisters apertando"Y".

Fazendo isso até o fim do jogo você ganhará também a conquista "Dealt with every Little Sister".