Large or complex systems tend to be challenging when it comes to managing their project and construction while keeping the costs at an acceptable level. Systems Engineering aims not only to reduce that difficulty by systematically owing down the top-level user needs to the bottom level parts specification, but also by describing the full aspects of its lifecycle. Moreover, together with Systems Management, they aid the completion of intricated projects, such as professional telescopes. This paper shows how Systems Engineering and Systems Management are helping the construction of one important instrument for the Giant Magellan Telescope: MANIFEST, which is a robotic fiber-optic positioning system that improves the capabilities of other instruments in the telescope. It can increase and even split their field of view into two or more instruments. Its Operations Concept is briefly explained, and the flowdown from the Observatory Architecture and the Science Cases, with their corresponding Science Requirements, is presented. Interfaces with other equally important instruments are described, such as GMACS, a wide-field multi-object moderate-resolution optical spectrograph, and G-CLEF, a high-stability, high-resolution, echelle spectrograph operating in the visible range of the spectrum. Managerial aspects of the processes and documents involved are also explained, as well as the next steps for the incoming Conceptual Design phase.