Yu-Gi-Oh! Go Rush!!

The Letter That Leapt Through Time (1x145)

:

There is a letter hidden in the wooden Duel Disk discovered in the Mutsuba Mountains. It's written by Yuamu in the Sengoku era, and addressed to Asaka in the modern age. It's a challenge letter, with the sequence for the Duel recorded on it. In order to reactivate the time machine, Asaka and Yuamu will clash across space and time!