Fast-neutron directional detectors using scintillating optical fibers have been adopted for neutron emission profile measurement in magnetic confinement fusion devices. Because of their benefits of rapid response and directional properties to reduce restrictions on shielding, they are anticipated for installation in the Large Helical Device (LHD) of the National Institute for Fusion Science (NIFS). As described herein, the system design has been re-examined based on the results of recent experiments and simulations. Results show that fast neutrons with high energy of 14 MeV are attenuated by a self-shielding effect of scintillating fiber. Moreover, it has been demonstrated that the scintillation photons are attenuated in several centimeters before reaching the photon detector. The control of the photon transmission efficiency is important to enhance the directional property of the system. Along with reduced effects of the background gamma rays, adopting a thin scintillating fiber is effective. Further evaluation should be conducted to design a detector system considering the detecting efficiency, directional property, and gamma ray effect for application to an actual radiation field of the LHD.