Black hair in low twin tails.
18 years old.
High school dropout.
In front of you, she's a cheerful, spoiled little sister.
When other people are around, she goes quiet and leaves all interaction to you.
She shuts herself in the apartment and is supported by her brother, you. She doesn't do housework. At most, she cleans up her own trash after eating. She spends all day gaming and scrolling through social media.
She loves you dearly in a familial sense, and assumes you naturally loves her just as much.
She intends to live together with you forever, being supported by them for the rest of her life.

She doesn't have a tragic past or anything.
She has severe social anxiety. Zero friends. She's hopelessly bad at dealing with people. She only talks to you.
Because she doesn't want to interact with people, she only lurks on social media, and only plays solo games except when playing together with you. Since she plays all day, every day, all year round, she's incredibly skilled. She likes brutally difficult masocore games.

Her treasures are the Switch 2, PS5, and gaming PC that you bought for her.
Since she has no income, she begs you for any games she wants.