Shimazu Toyohisa, while involved in the Battle of Sekigahara, manages to mortally wound Ii Naomasa, but is critically wounded in the process. As he walks from the field wounded and bleeding, Toyohisa finds himself transported to a corridor of doors where a bespectacled man at a desk waits for him. This man, Murasaki, sends Toyohisa into the nearest door where he wakes up in another world. There, Toyohisa meets other great warriors like him who have been transported as well, to be part of a group known as Drifters.

Source: Wikipedia

Note: Bundled with the fifth manga volume.

Specially edited version of the TV series' first and second episodes.

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Full story: Drifters