The battle pits players against Kanshou and Bakuya a pair of dragon monsters with 2,800,000 HP each in order to earn the legendary Twin Blades mentioned in the event's lore. The battle however has a slight complication in that Kanshou and Bakuya are immune to Magic and Physical attacks respectively. They also have high DEF and SPR values each, so even trying to hit them with the adequate form of damage will likely not yield good results.
In order to damage the Bosses the player needs special abilities granted by the Bosses themselves. Kanshou's Wrath and Bakuya's Vengeance which will reduce the opposite boss' DEF or SPR by a significant value making them much more vulnerable to damage. For this to happen the bosses will use the equally named abilities on units on the party (as a single target damage that decreases that unit's DEF or SPR greatly), then the unit hit with the attack can use it on the next turn.
The special abilities deal fixed damage against the bosses of roughly 1.5% of their HP (these abilities can be used twice if one Dual Wields) and the goal of the battle is to weaken both of the bosses through these abilities, damage them (but not kill them) with regular abilities, and then finish both of them during the same turn through these special abilities.
Both of these bosses can use either Black/White Mist (Magic Damage to all units), Savage Bite (very strong physical damage to one unit) or Tail Swipe (Physical Damage to all units). Then followed by their special ability and normal attack.
Both Bosses have no elemental weakness/resistance, are immune to all status ailments and are vulnerable to all stat breaks.
The battle is not really difficult and mostly long and tedious due to the aforementioned mechanics. The player should bring both physical and magic damage units for best results one of each kind suffices, tho if the player can afford it, two of each kind will very much guarantee damage. Hybrid Damage helps but part of the damage will be mitigated.
A Cover Tank is useful but isn't mandatory, however a Magic Tank is most recommended as it deals higher damage. Mystea, Basch or the event's featured unit Chow work perfectly. Buffers like Ramza, Roy or Lunera are effective, however they can gain the special abilities while singing so that can drag things longer than necessary.
With defensive buffs up on the party and offensive debuffs on the bosses, the player should have more than enough to survive the attacks. Patience will be required as depending on the party's setup and luck, it may end up soon or late, but overall the battle poses little threat.