She looked at him. Really looked. “He wasn’t you.”

If you intend to write in this sub-genre, you must walk a tightrope. The market is fickle. Amazon’s algorithm has been known to "dungeon" (shadow-ban) books that use the words "brother" and "lover" too closely together.

The popularity of cannot be dismissed as mere shock value. Reader psychology reveals deeper needs:

In that moment, there was a deep realization of how much their familial bond meant to them. It was a connection that had blossomed from years of mutual support and shared history, providing a sense of security that was both familiar and enduring.

Liam and Elena weren’t bound by blood, but they were bound by a lifetime of shared secrets. Their parents had married when Liam was ten and Elena was eight, blending two fractured families into one. For years, they were the perfect team—Liam the protective older brother, Elena the spirited younger sister.

Authors use sibling relationships to explore deeper psychological and social themes: