Line capture devices for unmanned aircraft, and associated systems and methods are disclosed. A system in accordance with a particular embodiment includes a line capture device body having a line slot with an open end and a closed end. A retainer is positioned proximate to the line slot and has a rotor with a plurality of rotor arms positioned to extend at least partially across the line slot as the rotor rotates relative to the body. A joint rotatably couples the rotor to the body, and a ratchet device is operably coupled to the rotor to allow the rotor to rotate in a first direction and at least restrict the rotor arm from rotating in a second direction opposite the first. In other embodiments, the retainer can include other arrangements, for example, one or more wire-shaped elements.