Lenus is one of the major boss battles in the game. She is seen using the Blue Sea Dragoon Spirit.
 Strategy - First Encounter
Hit Points: 3400
Lenus is first encountered in the Twin Castle. She has many high-powered magic attacks that hurt painfully, paired with a high Magic Defense. For this reason, high-powered physical attacks help a lot, but generally come with the cost of low Magic Defense. In turn, using characters with a high Magic Defense will not do nearly as much physical damage to her. Dart's Fire-based magic can help a lot in this battle, especially Final Burst, as well as Fire-based Attack Items. If you have Albert, his Rose Storm is helpful. Just hit Lenus with as many attacks as you can and eventually she will lose the battle.
 Strategy - Second Encounter
Hit Points: 3000
Hit Points: 3200
In the second encounter with Lenus, she is paired with the Blue Sea Dragon, Regole on the Prison Island. It is probably best to kill the Dragon first, and then move on to Lenus, due to Regole's powerful attacks. His most painful one is when he summons a tidal wave to blow the party away, causing heavy damage to Dart and any low-Magic Defense characters. A good Final Burst attack will hurt Regole badly, and with powerful physical attacks, he should be defeated fairly easily. Lenus is then the target. She has overall higher defenses than her Dragon, and so takes less damage. However, she is still defeated without too much trouble. Once again, Fire-based Attack Items as well as Dart's Dragoon magic are helpful against her. Keep attacking, and eventually Lenus will fall.