We study semi-stable degenerations of quasi-Fano varieties to unions of two pieces. We conjecture that the higher rank Landau-Ginzburg models mirror to these two pieces can be glued together to lower rank Landau-Ginzburg models which are mirror to the original quasi-Fano varieties. We prove this conjecture by relating their Euler characteristics, generalized functional invariants as well as periods. We also use it to conjecture a relation between the degenerations to the normal cones and the fibrewise compactifications of higher rank Landau-Ginzburg models. Furthermore, we use it to iterate the Doran-Harder-Thompson conjecture and obtain higher codimension Calabi-Yau fibrations. 2 CHARLES F. DORAN, JORDAN KOSTIUK, AND FENGLONG YOU 9. Gromov-Witten invariants 36 9.1. Orbifold Gromov-Witten invariants 36 9.2. The formal Gromov-Witten invariants of infinite root stacks 37 9.3. Mirror theorems 38 References 40