The elemental mixing topic got me thinking about Merton - some about the etymology, Thomas Merton perhaps? - but mostly why isn't this Terra's most powerful spell instead of Celes? Here are some supporting arguments:
- Terra learns Fire spells naturally, and Maduin (her father) is the wind esper, so a fire/wind combination makes quite a bit of sense;
- Terra is a quasi-religious figure due to her unique birth, transformational powers, and frequent characterization as a savior, so her being the Crusader fits thematically;
- Crusader is obtained in the Fanatic's Tower, which is also where her pendant is found in the WoR, maybe there's some attraction between the two?
- Like Merton, the Crusader summon hits all targets on the battlefield, which exhibits Terra's difficulty in controlling her powers.
Furthermore, Celes using Ragnarok/Ultima aligns much more with her storyline as well (besides the fact that Celes looks of Nordic ancestry):
- The Ragnarok myth correlates pretty strongly with Celes experience upon awakening in the WoR;
- The Ragnarok summon is just a sword, appropriate for Celes the soldier;
- Non-elemental Ultima is the logical progression from ???
Arguments against are:
- Ragnarok is (currently) found very late, so that reduces the potential utility of the Stam/Speed esper bonus for Celes (see spoiler below);
- It removes Celes access to fire-elemental spells, but I don't see this as a huge drawback.
To address some of these drawbacks, you could:
obtain Ragnarok by defeating the Water dragon (rather than the Holy dragon for Crusader), since the Sunken Castle story also closely parallels the Ragnarok myth (great battle, death of Odin, world submerged by water, two lovers). Then Crusader would be obtained by defeating Kaiser dragon, which is more in line with how Crusader was originally obtained by defeating all the dragons; and since Merton is not that great a spell, it's not a big deal if it's obtained late. It also makes sense for Crusader to be obtained just before facing the statues, since the summon is depicting the battle between the Warring Triad.