My Big Sister is an RPG-like horror adventure game about two sisters: Luzia, a sarcastic twelve year old, and Sombria, her older sister.
- Brick Joke: Over the course of the game, there's multiple sinks to inspect. All of them are useless except for the one in Chapter 10, where it has a loose pipe in it.
- Cigarette of Anxiety: Sombria has a smoking break at one of her hospital visits to Luzia.
- Chekhov's Gun: Uncle Bob's screwdriver, which is mentioned to be in a drawer in the second chapter, is used in the eleventh chapter to screw off the hinges of the basement drawer.
- Deadpan Snarker: Luzia is a young girl full of sarcastic one-liners.Luzia: Huh, it's a sink. That's pretty neat. If anyone is listening to me right now, I'm using sarcasm!
- Driven to Suicide: If you immediately use the bobby pin to unlock Sombria's door in chapter 11, you'll discover that this is Sombria's fate.
- Luzia in the beginning keeps having a dream where Sombria is a ghost. Later Sombria becomes an undead yokai.
- On the train ride, there's a scene of Luzia in a coma flat lining while Sombria takes a cigarette break. This scene is relevant for two of the endings.
- "Groundhog Day" Loop: A possible explanation of the curse is that Sombria created a loop due to her depression over her sister's death.
- Opposites Theme Naming: Sombria is a Spanish word with multiple meanings, including "Somber", "Shadowy", and "Dark". Luzia is a reference to a play of the same name by Cirque du Soleil, with said name being a made-up portmanteau of the Spanish words Luz ("Light") and Lluvia ("Rain").