Lyla

A wicked monster looking like a one-winged angel appearing in the Collaboration Scenario. She comes from Parade Buster with Lest, Musette and her partner Bell.

Biography
She first appears near the end of chapter 3 with her partner to attack Lest and Tarsa under order from the Queen of Dreams. They lose, but reappear a bit later when they reveal that Musette has brainwashed the Grand Noah Queen, and have Tarsa incapacitate Lest to imprison him while using the disguised succubus for nefarious purpose.

She shows up again with her partner and her boss during chapter 8, when Kazuya's party has beaten Fulbeua in the Château des Romances. As Musette orders Fulbeua to dispose of the party, Bell and Lyla are shocked by the insolent nightmare who refuses to follow the order and who resists Musette's brainwashing. The conflict allows the party the time to escape.

She reappears again during chapter 10 when the Alliance of the Queen of Dreams prepare her plans. She, Musette and her fellow consider themselves the only ones really loyal to Est, and thinks of the others as nothing more than lowly misfits.

The party is forced to fight the full trio during chapter 12 as Musette and her partners try to hold the party back from Est's Land of Nights. They then tell that they held no loyalty to Est and intended to backstab her to get the world for themselves. They are ultimately routed by the heroes, marking the beginning of the collapse of the alliance.

The trio returns one last time in the post collab, where they got to Snow Shrine with Daimyokai in hot pursuit. The party meets them at the entrance, and after a fight that ends in the hero's favor, the Grand Noah Queen says they have no choice but to recruit them in the Pocket Castle as Grand Noah guards wouldn't be able to resist their brainwashing techniques. As Musette accept to join the hero's group, both Bell and Lyla oblige out of loyalty for their leader.

Monsterpedia entry
"A being who arrived from another world. Further Details are unknown."

Attacks

 * Attack – One Foe, Physical Attribute
 * Explosive Fist – 4 Random Foes, Physical Attribute
 * Magi's Unite – 6 Random Foes, Physical Attribute
 * Gale – All Foes, Physical, Wind Attribute
 * Melty Kiss – One Foe, Pleasure Attribute, Horny (75%)
 * Proselyting Fellatio – One Foe (M), Pleasure Attribute
 * Chest of Paradise – One Foe (M), Pleasure Attribute
 * Pleasurable Intercrural – One Foe (M), Pleasure Attribute
 * Hustle Dance – All Allies, Heal, +800 Speed
 * Hip Attack – One Foe, Pleasure Attribute, chapter 3 only
 * Forceful Buttjob – One Foe, Pleasure Attribute, chapter 3 only

Chapter 3
With a party of two, the options are quite limited.

Lest will be the main damage dealer thanks to his heroic skills. As they have extremely limited crowd control, charging attacks to fully exploit his potential is possible.

On lower difficulties, they can be reliably stunned by Tarsa's scream for three turns. Afterwards, the latter's role is just to keep Lest alive and buffed.

If you have difficulties, leveling will help a great deal. At level 54, Lest will get Flash Counter which sets up a powerful counter against most of their attacks, while Tarsa gets a powerful buff with humming.

First and Second Battle
This time, she appears with Musette and Bell. Fighting the trio can be tough thanks to their numerous status effects. Preventing them can help keep a steady damage flow and make sure your healer is always at the ready. They have different weaknesses, but they don't cover each other. Simply avoid using holy, dark, wind and pleasure attacks if you target the whole party.

It can be worth it to focus on Lyla with Ice Spells as she can use a party-wide heal. She doesn't use it on a regular basis, but removing her from play both reduce the damage and can prevent the fight to drag on.

The second battle is identical, except they all have +100 to their stats, making them slightly more dangerous.