The Alterspire (A World Apart in the European Version) is Chapter 24x of Fire Emblem: Shadow Dragon.
This chapter is the only chapter to contain enemy Berserkers, Swordmasters, and Warriors, (except for the chapter The Lair of Fire, where Ymir is an enemy before you recruit him) although you can fight units of these classes in the arena.
There is a way to enter this chapter without losing Falchion. First, the player must have Tiki hold onto Falchion. Second, they shall allow her to be killed in or before Chapter 24. At the end of the chapter, Tiki is dead and Falchion is gone, so Gotoh sends the group to 24x. But, since Tiki died while holding it, the good Falchion will be in her inventory. Third, then, the player must use the Aum staff to revive Tiki. Following this, it is possible to enter the Endgame with two Falchions and two Divine Dragons.