The FeSe nematic phase has been the focus of recent research on iron-based superconductors (IBSs) due to its unusual properties, which are distinct from those of the pnictides. A series of theoretical/experimental studies were performed to determine the origin of the nematic phase. However, they yielded conflicting results and caused additional controversies. Here, we report the results of angle-resolved photoemission and X-ray absorption spectroscopy studies on FeSe detwinned by a piezo stack. We fully resolved band dispersions with orbital characters near the Brillouin zone (BZ) corner, and revealed an absence of any Fermi pocket at the Y point in the 1-Fe BZ. In addition, the occupation imbalance between dxz and dyz orbitals was the opposite of that of iron pnictides, consistent with the identified band characters. These results resolve issues associated with the FeSe nematic phase and shed light on the origin of the nematic phase in IBSs.Twinning is a phenomenon which describes the intergrowth between two identical crystals, and can complicate the analysis of their intrinsic properties both from a physical and structural perspective. Here, the authors use a piezo stack to detwin FeSe crystals and then investigate the band dispersions using photoelectron and X-ray absorption spectroscopies in order to further clarify the origins of the nematic phase in FeSe.