The Alterspire

''"Marth did as Gotoh instructed and chose soldiers for his journey into the unseen. What lay within the tower in this alternate world to test him? Marth's heart wavered. But with neither the divine blade Falchion nor the divine dragon girl to aid him, the tower's master was his last hope of defeating Medeus.

Gotoh had told Marth to find a coffin. So while most of his companions remained in the material world to battle Doluna, Marth and his chosen few scoured the tower to search of a mysterious savior."''

Information
A World Apart is chapter 24X of the game Fire Emblem: Shadow Dragon.