Slightly exploring the game Her Tears Were My Light, based on memory. Spoiler warning.
Once the game is started, the player meets Time.
Time is a girl who cares about her friends and is kind. Her ability is pretty much time travelling- she can go forward or backward in time to any moment she has already experienced in the current playthrough.
Very quickly in the game, she meets Space.
Space is complicated, which anyone who has completed the game would likely understand.
There are two versions of Space: Space, and Nil.
These two versions are each other's opposite.
Space exists to put something where nothing is- her ability is to create stars when she cries. Nil exists to put nothing where something is- and while this means she can erase Space, she also has the ability to trap Time temporarily by limiting how far back she can rewind time until the player gets Time out of that situation.
Space is extremely innocent, while Nil is affected by how she became Nil. Nil spends most of the game acting on her want to erase Space.
Nil exists because of Time. There is a part of the game where Time shows Space her ability by rewinding to before Space cries in front of her, which is where Space becomes Space and Nil. A copy of Space is left in Space's body, and the original Space is pushed out, becoming Nil. Nil wants the copies of Space gone so she can have Time to herself.
Nil isn't exactly mean, but very driven by her emotions and wants. This at first makes Time want to save Space from Nil after she first finds out that Nil keeps erasing Space, and she is supported by each copy of Space each time.
The player eventually reaches two endings: Space's ending, and Nil's ending. Each girl's ending has Time spend the rest of eternity with just that girl, and both endings are able to be achieved in the same playthrough if the player decides to go back for the other girl, the one that Time doesn't spend the rest of eternity with. Being with Nil, getting Nil's ending, is how the player learns her story.
There is one final ending: the True ending. It is an ending where Time spends the rest of eternity with both girls. After getting it, the player can restart the game, wiping the memories of all three girls, and ending up right where they started.
