The Archylte Steppe becomes a very different place when thunder rolls across the heavens, for it heralds the coming of Yomi, one of the host of the Undying that is also known as the Wings of Death.
Why does it only appear with the lightning? The answer lies in its former life. Yomi was once a great hero, driven to prove that he was the most powerful warrior of his age, but he was struck down by lightning on the steppe before he could complete his quest.
Now he wanders the very same steppe where his life was so suddenly cut short. Amidst the crashing thunder and howling wind, no one hears his tormented screams.
Yomi could be considered a weaker version of Vercingetorix from Final Fantasy XIII since he has nearly 1/13 of Vercingetorix's total HP, and the strategy to deal with Yomi is no different. Like Vercingetorix, Yomi uses powerful Wind attacks and erects a barrier, called Impenetrable Aura, that makes it temporarily invulnerable, heals it from status ailments and partially restores its HP. Once Yomi's HP drops Yomi will get more aggressive and sprout more wings and will not use Impenetrable Aura as often. At this stage it will focus on using Wind Shear or Putrescence.
It is recommended to have Serah and Noel with at least 5000 HP, and a fully developed Crystarium helps greatly. The party can wear offensive accessories and it is good to equip Serah's Sagittarius and Noel's Mac an Luin since they allow one to queue six commands into the ATB bar.
The most efficient monster to defeat Yomi is the Cactuar. It has a high attack and learns all of the passive abilities that work well against Yomi, namely Bravery Feeder, Deprotect Chaser, and Protect Feeder. The Cactuar's sky high attack damage can reach up to over 1,500 and its quick attack speed adds to its overall effectiveness. Since the Cactuar is small and jumpy, a good portion of Yomi's physical attacks will miss it.
One way to start the battle is with SYN/SYN/SEN and buff while Yomi's attention is drawn to the Sentinel. If the party has Goblin Chieftain they can use his Feral Link to buff from the start. After being buffed the party can switch to a paradigm with Saboteurs and debuff Yomi. Poison drains Yomi's HP fast, seeing as Yomi has such high max HP, but it is difficult to get it to stick. If the player wants to poison Yomi they should focus one character on casting Poison until it works. Imperil is another useful status to apply. If the player doesn't want to use Poison, they can just debuff Yomi with Deprotect and then attack with physical attacks, but one may as well apply Deshell and Imperil to speed up the process.
When Yomi uses Impenetrable Aura it heals itself from all ailments and starts restoring its HP, but once it gets out of this state the player can start spamming debuffs again. Whenever the party loses the buffs due to Putrescence the player should switch back to SYN/SYN/SEN. The best moment to heal is when Yomi uses Impenetrable Aura. The Sentinel can be useful for most of the fight. If Yomi uses Wicked Whirl the party should switch to SEN/SEN/SEN to minimize damage and switch to MED/MED/MED to restore HP.
Yomi is the Japanese word for the Land of the Dead. In Shinto mythology, it is related to the Kojiki where the dead go to delve and rot indefinitely.