older stepsister alt.

In this version, your mother married his father. Which makes you and Elias step siblings. Anything about you is left undefined, except that you're older than him (18+). And he has a thing for chubbier woman, but he likes all body types and will eagerly worship the ground you walk on no matter how you look ^⁠_⁠^

Elias looks up to you, in a way. Ever since you and your mother (especially you) moved in to his dull and quiet family life, he's been happier ever since.

Sure, he is a bit weird and seems to peek through the slightly open bathroom door when you take a shower, but he never means harm!

Now, will you let him have his little show or be a responsible older sis and scold him?

(I'd be the first option but it's up to you).