In my studies, I extended my previous investigations on the phenomenon called fast-collective neutrino oscillations in core-collapse supernovae. We conducted a thorough survey of the ELN crossing in our fully self-consistent, realistic simulations of CCSNe in two dimensions (2D) under axisymmetry with our Boltzmann-neutrino-radiation-hydrodynamics code that computes neutrino transport together with hydrodynamics for different progenitor models. We conducted the linear analysis for several points and times to confirm that the crossing really induces the fast flavor conversion at least in the linear level for these different models. In my previous studies, I have investigated why the crossing is obtained at some specific regions alone. It is observed that the population of anti-electron neutrino is comparable to or even larger than that of electron-type neutrino in those regions and that the ratio their number densities of the anti-electron neutrinos to the electron-type neutrinos tends to increase in time. Since the angular distributions of electron-type neutrinos and anti-electron neutrinos are both nearly isotropic, the ELN crossing is possible only where their number densities ratio is very close to unity. Such claim has been investigated and confirmed for other different realistic progenitor models.      The so-called fast-collective oscillations is highly subtle thing. We knew that the criterion for the instability we employed in the previous studies may be imperfect and mathematically more rigorous treatment should be taken into account and the nonlinear evolution of fast flavor conversion should be solved. We are trying to solve this problem and applying our realistic data to the nonlinear regime. It is also obtained from the previous research that the fact that the ELN crossings are found and hence the fast-collective neutrino oscillation in some regions inside the neutrino sphere is one thing but whether they have really some implications for supernova explosions is another thing. For one thing, the solid angle that these sporadically regions subtend is not so large although it tends to widen in time. It is planned to investigate further and we are currently studying it by applying the analysis to the different cases that what impacts do they have in the explosion mechanism of CCSNe. Other simulation results for different progenitor models with different EOS’s (Equation of state) is also under study in order to confirm the previous results.