Loyalty in what gets called the 'Luffy harem' is fascinating because it's never romantic or exclusive in the traditional sense. It's a one-way, absolute devotion to him, but not from him. Boa Hancock's loyalty is obsessive and possessive, but she knows she's one of many orbiting him. She's loyal to the idea of him, not to a shared bond. Meanwhile, characters like Nami or Robin are fiercely loyal to Luffy as their captain and friend, but their devotion exists completely outside any harem context—it's crew loyalty. The structure itself is built on Luffy's obliviousness; he's the fixed point, and the loyalty flows inward without expectation of reciprocation. It creates this weirdly stable dynamic because there's no jealousy-fueled conflict—everyone's just trying to support his dream, even if their personal feelings differ.
The portrayal ends up highlighting a very specific kind of loyalty: self-sacrificing and often humorous because it's so unrequited. Hancock would destroy a country for him, but he'd just ask if they have meat. It's less about romantic fidelity and more about an extreme, almost ideological commitment to his person and goals. The loyalty isn't between the 'harem members' either; they don't form a sisterhood. It's a series of individual, intense connections to the same center point, which I think is why the term 'harem' feels a bit off. It's more like a solar system with a very hungry, rubbery sun.