Fast radio bursts (FRBs) are an enigmatic phenomenon; trains of coherent radio waves are arriving from a cosmological distance for a millisecond. The most promising source of FRB is neutron star (NS). In fact, very recently a low-luminosity FRB has been detected from a strongly magnetized NS, SGR 1935+2154, simultaneously with an X-ray flare. Focusing on the NS model, I will describe the theoretical insights and challenges that such observational achievements have implied : “What is the emission mechanism of FRB?”, “What type of NSs can be the source of FRB?”, and “How such NSs are formed with what type of explosive transients?”. Finally I will discuss prospects and strategies to provide a comprehensive answer to these questions.