Type Ia supernovae (SNe Ia) are thermonuclear explosions of a white dwarf (WD). Despite the intensive use of their light curves as the matured standard candles, the origin of SNe Ia has been obscured. Recent accumulating data have been revealing their diverse natures in various observables, and a picture is emerging that SNe Ia are not at all a homogeneous system but represent multiple systems regarding their progenitor evolution and explosion mechanism. It is thus important to specify the progenitor and explosion mechanism for individual SNe Ia, in order to understand their nature as a whole population. One of the powerful methods to reach to this goal is provided by intensive observations of SNe Ia in the first few days. In this talk, I will first present ideas to use the early phase observations to discriminate different scenarios. Several specific SN Ia examples are shown, including an SN Ia discovered within the day of the explosion by our systematic search of infant SNe Ia using the Subaru/HSC. Finally, I will summarize perspective for Subaru/HSC and also for the combination of Tokyo/Tomoe and Kyoto/Seimei telescope for this study, and also possible collaborations using DEcam and LSST.