Transients with fast brightness variance in UV/optical wavelengths (”fast transients," such as early-phase supernovae, fast blue optical transients, kilonovae) are of great interest in astronomy. Although great progresses in time-domain astronomy have been made via wide, shallow, and day(s)-cadence surveys, the limited observing depth and low time resolution make traditional time-domain surveys difficult for fast-transient studies. In this talk, I will introduce our previous/ongoing studies of early-phase type Ia supernovae and fast blue optical transients via deep (Subaru/HSC) and high-cadence (Kiso/Tomo-e) wide-field surveys. As one of the most powerful transient survey facilities in the 2020s, the 2.5m Wide Field Survey Telescope (WFST, or "Mozi") took the first-light image on Sep 17th 2023 and started a pilot survey recently. I will then briefly talk about transient studies through the ongoing WFST pilot survey and the role that WFST will play in the golden era of time-domain astronomy.
