Proper Fae build

If I understand, you play her with Nowi and A.Tiki. We don't care about Fae's matchups against Falchions because we expect all losses; Falchion gets +70% atk against her for effective damage + weapon triangle advantage. Fae doesn't even have that good of def unless you really go for it.

Here's my interpretation of Fae: if you're going to invest in her speed, you need to go hard. +spd IV, +spd weapon (probably lightning breath if she's playing with A.Tiki and Nowi; she's the best at handling mages of the three due to her natural res being highest and red mages being the least common plus Nowi can handle those), ally support with one of the two (probably Nowi), receiving hone dragons or at LEAST goad dragons, maybe fury. This way she gets to 40-45 spd before merges (and you can even add summoner support if you want) which blocks almost any double besides bold fighter. A.Tiki should probably handle those by using guard. She has excellent def anyways. The reason is that if Fae takes +spd IV and +spd on her weapon, she's sitting at 25 def before skills and merges, which isn't good. That's barely enough against blues, and maybe not enough if there's a bold fighter bonfire/ignis coming at her, so taking them on enemy phase would not do. She won't necessarily be able to win against Hardin on her turn if the guy is receiving ward armour because his res is good to begin with and people tend to recommend warding breath for him. However, if you push her spd and she receives hone/goad dragons, she has some chance against him on her turn.

The other option is to invest a lot in her def, in which case she wants +def IV, +def weapon, and probably steady breath. Now she has 37 def before ally support, buffs, and a seal, which is quite solid. If she's going to be the main mage tank on the team, then she should use either +def refine or warding breath along with distant def seal for 39/40 ranged def, which should be enough to tank two hits along with her thick HP pool.