Warmth in Snow

After departing from Clow, the first new world the travelers land in is ruled by three royal sisters. A kind princess, her deadly protector, and a secretive priestess. Though they seem friendly enough, it is clear that there are secrets in their kingdom, and the truth the travelers discover may be one that they end up regretting looking for.

A Tsubasa Reservoir Chronicle (by the wonderful CLAMP) fanfiction taking place after the final volume and before the start of Tsubasa World Chronicle.