What starts as just another school day for Sakura quickly becomes something more when first Eriol announces that he’s moving back to England and then Shaoran makes a shocking announcement of his own.
A romance-focused bridge between the movie conclusion of the first series and the 2018 continuation. If you haven’t seen those earlier works the character references here won’t make much/any sense.
More Information:
aniDB
Crunchyroll
Wikipedia