OMG OMG OMG!!
THANK YOU SO MUCH FOR SUCH A LOVELY COMMENT! T__T <3333
You are really sweet for not wanting to hurt the character, for some people it's the very first option XD
Yes, the Other remembers things, but some are more impactful than others. Breaking stuff is something they'll reference a lot, especially if scared XD The reactions change depending on what you've done previously and which room you are currently in.
Story is something you create/discover when you use the same action twice: the Other tells you a part of your mutual story and it gets written on the walls of the main hall. Basically, Story is the in-game experience where you discover who your "character" is and what kind of relationship they have with some particular Other.
Afterstory is seen through the change in the VO style (I talk with my normal voice through the "phone" filter) and the character of replies :) And it's about the outside-of-the-game reflection. To simplify, in the Story the Other talks to your character, in the Afterstory I am the Other is talking to you ;)
There is no real "game ending", because you can stop at any moment and it's ok. Technically, you can consider the game absolutely "finished" when the Other runs out of new replies to any of your actions. If you can't do anything new, it's kind of done XD
But "finishing" the game is also a choice. There are many options for the player's motivation to do or NOT do things.
It's an art-game, an art-project. So the main goal is to make you feel and think. But if someone perceives it as a game in which you have to unlock all the content and get an "achievement", that also says something ;)
P.S. You don't have to hurt the Other is you don't want to, but your friend absolutely can.