Letter of Challenge - S1.E10

Having inherited BB's wishes, Seigi takes Wiseman's advice and lies low in a mountain hideout for a year. Izzy and Tom have spent the year with him, along with Tamaki, who joined them on the mountain, and Seigi has finally grown strong enough to overpower Izzy. Then one day, a mysterious enemy attacks their hideout, leaving behind a video letter with footage of Arya in America, near the location of the third ruins.