Primarily responsible is Enmu, the Lower One of Muzan's extremely powerful demons in the Twelve Kizuki who we meet at the tail end of the first season, who is able to put ticket holders into a deep sleep, making it easy for lesser demons who make it on the train to, uh, eat people.
The Winter calendar is lit! The manga series was rated the best-selling in the year 2020.
It isn't bad, but by Demon Slayer standards, it falls short of that extra oomph factor plot-wise.