The eternal frost

The world has been hit by a second ice ages, humanity still persists relaying on heaters call hearts, each city has its own heart but people can buy small personal ones, these heaters are blood powered, Lucky for us when the ice came so did the wraths, these furry cat like creatures the size of a fully grown horse and with sword like teeth. Theres a train that runs supplies between the cities, it's called the ice run,