The End of You is a lo-fi mood piece that features a total of 12 achievements. Since a laid-back playthrough takes half an hour at most and a second run is needed to get the other ending, it is recommended to go in blind the first time and check the guide to get the missing achievements the second time around.
Explore all the rooms of your flat after waking up and hug Emily once she appears in the kitchen. Every time you pick up one of her belongings -seven in total-, she reappears somewhere in the flat and waits for your word. After every chat (and dropping the item to the relevant box), either explore your flat ('Optionals') or look for the next item that reminds you of her ('Belongings').

These can be done anytime after dropping a belonging but before picking up another one.
Get close to the door of your flat and take a look outside.
Throw any pickable object from the balcony onto the car parked below. A book would do nicely. There is also a stack bricks right there at your feet.
Listen through all five cassette tapes found by the hi-fi in the living room.
Inspect all twenty-five books found within your flat. Twenty of them are placed in the bookcase in the living room. Two more are by the window next to the said bookcase. 'Moreschi' is found on a table in the same room, while 'Castration: A History' is laying on the nightstand in the bedroom. Finally, there is 'Endo and You' (that doubles as a belonging, i.e. 'Emily's book') in the bathroom.

These are directly tied to certain belongings thus must be done at specific points.
Throw one of Emily's belongings off the balcony. Don't worry, it comes back.
Play 'Emily's cassette' via the hi-fi in the living room before disposing it. Likewise, once you get hold of 'Emily's VHS', watch it through the tape player found in the same room before boxing it.
After inspecting her cigarettes but before talking to Emily, interact with the ashtray next to her. Similarly, after inspecting her toothbrush, step into the bathtub before having a word with Emily.

Since the game offers no checkpoints, a second playthrough is needed for 100% completion.
After collecting all of Emily's belongings, she appears for the final time in the bedroom and asks you a question. Your answer decides the achievement you get and locks you out of the other.
No matter your answer, instead of locking away Emily's box, go to the balcony and throw it out.
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'You deserved better. Someone who could take care of you.'