Type Ia supernovae (SNe Ia) have been used as "standard candles" to demonstrate the accelerating expansion of the universe while the nature of their progenitor systems and how stars explode are still obscured. Photometric information of SNe Ia within a few days of their explosions (hereafter early-phase SNe Ia) plays an important role in solving such long-standing issues of SNe Ia, and the systematical study of early-phase SNe Ia is now carrying out with the new generation wide-field camera mounted on the 8.2-m Subaru telescope—-the Hyper Suprime-Cam (HSC). In this presentation, I will report an abnormal early-phase SN Ia, MUSSES1604D (SN 2016jhr) discovered in the first observing run of the "MUlti-band Subaru Survey for Early-phase SNe Ia" (MUSSES). Our study indicates that the strong but red flash at early phase followed with peculiar spectral features of MUSSES1604D only can be naturally explained by a supernova explosion triggered by the helium detonation at the surface of the progenitor star. This discovery is the first evidence of the He-shell detonation scenario and clearly indicates the multiple origins of the early light curve excess of SNe Ia. In the second half of the presentation I will talk about the diversity of the "early-excess" features in terms of previous observations and the future plan of MUSSES. With the powerful survey capability of Subaru/HSC, we expect to catch a promising number of "early-excess" SNe Ia in a few of years, which will help us to figure out how different scenarios play in generating these special early-phase signals and their connections to the diversity issue of SNe Ia.