// The relationship declaration
#[derive(Component)]
#[relationship(relationship_target = HairOf)]
pub struct HasHair(Entity);

impl HasHair {
    pub fn new(hair: Entity) -> Self {
        HasHair(hair)
    }
}

#[derive(Component)]
#[relationship_target(relationship = HasHair)]
pub struct HairOf(Entity);

// Setup
let hair_entity = commands.spawn(Hair(character.get_hair())).id();

commands
    .entity(character_entity)
    .insert((
        Name::new(character.get_name()),
        HasHair::new(hair_entity),
    ))
    .add_child(hair_entity);



// later in a system
commands.despawn(character_entity);