This fight is easy, as it is a tutorial battle. The player can simply use the Songstress abilities to limit Logos's actions and pound away at him with physical attacks. Ormi deals more damage than Logos, but Logos can use Potions to heal himself or Ormi.
The party should focus all attacks on Logos's companions first before taking him out.
Logos gets a bit harder here. The party should bring several Eye Drops and Echo Screens to counter Silence and Darkness. If the party has Sleepy Shuffle, it may be useful as Logos only has a 30% chance to resist it, and makes the fight that much easier.
The player can use the same strategy as in the third encounter.
In the final two fights, Logos should be defeated first, as his Russian Roulette is deadly as it can inflict Death or Petrify. Employing a captured fiend that knows Ailment Def., such as a Tonberry or Kukulcan, is recommended to block the negative status effects that Logos can inflict with Russian Roulette. The Kukulcan comes with the added benefit of being able to use its Heaven's Cataract move, which can deal major damage to Ormi and Logos and lower their defenses.
The player can use the same strategy as in the fifth encounter.