While looking for Treasure Tools in Friagne's old hideout, Yuuji and Shana seemingly swap bodies due to the Treasure Tool Reshuffle. They must now go back to Yuuji's house and return to normal without their friends or the other Flame Haze catching on to their situation, all the while feeling a foreboding from Alastor's warnings.

(Source: Shakugan no Shana Wikia)