Distinct love interests
Reverse harem's core craft challenge is creating multiple love interests who are genuinely, thoroughly distinct: not just different on the surface (tall/dark/brooding versus blond/sunny/playful) but different in their emotional architecture, their history, the specific needs they bring to the relationship, and the specific way they connect with the heroine. Each man should fill a different emotional space in her life — not the same romantic need in different packages, but genuinely different forms of connection. The reader should be able to name each love interest's specific appeal without overlapping with any other, should be able to explain what the heroine gets from each that she cannot get from the others.