Tsubasa: Spring Thunder Chronicles, Tsubasa Reservoir Chronicle OVA, Tsubasa Reservoir Chronicle: Spring Thunder, ツバサ 春雷記Page 1
A 4 part OVA released with the limited editions of the Tsubasa and xxxHOLiC volumes.
There are two OVAs for each series, with plots linked together.
They cover the Nihon Country Arc and scarcely some of the Celes Country Arc.
(Source: Official Project Website)