Millianna

Millianna is one of Erza's childhood friends from their days as slaves working on the Tower of Heaven, and she briefly worked as one of Jellal's minions for a time. She is an avid cat lover, having decorated her entire room with a cat theme; her love of felines is to the point that she refuses to hurt anything that even resembles a cat, even if she knows that it is not a cat.

History
Millianna was one of the children who were taken from their homes and forced to build the R-System, aka the Tower of Heaven. It was there that she made friends with Erza, Jellal, Wally, Shou and Simon, and together they weathered the cruel "motivation methods" of their captors. One day, Erza decided it was time to fight back and inspired the other slaves to stage a revolt. Despite some sacrifices, the slaves were successful and set to leave the island for good. But Jellal, now being controlled by Zeref, destroyed the ship leading off the island and claimed it was Erza's doing to convince Millianna and her friends to stay and finish the tower. After eight years, the tower was finished.

Tower of Heaven Arc
Millianna first appears at the casino where Team Natsu is currently vacationing, where she ambushes Lucy, tying her with her rope and having it tighten around Lucy every few seconds. She then regroups with the others as they kidnap Erza (As well as Happy, who Wally gives to her as a present), and together they set off to the Tower of Heaven. Later when Natsu's group invades the tower, she fights against Natsu alongside Wally in her room. At first she is unwilling to attack him since he is wearing cat mask (Natsu was fooling around with it when he first entered the room), but after Wally convinces her Natsu the enemy, they double team him and manage to gain the advantage. Happy saves Natsu before Wally can kill the Dragon Slayer, however, and his presence causes Millianna to hamper Wally's attacks. A final cuteness attack by Natsu distracts her enough to loosen her rope around him, and this allows Natsu to knock both of them out.

Later, at the insistence of Simon, she and Wally carry out Lucy and Juvia, then along with Shou, Happy and Gray, they leave the island just as the Aetherion comes crashing down on the tower. The group can do nothing but watch from afar as a series of tumultous events unfold, not the least being Natsu and Jellal's destructive battle.

Afterwards, Millianna reconciles with Erza and apologizes for her actions, all while mourning Simon's demise. Erza invites the group to join Fairy Tail, but while they consider it at first, they stow away the night they're supposed to head back, still feeling ashamed of what they've done. Erza finds out but doesn't stop them, and allows them to go. However, this is not not before giving her friends a grand sendoff with fireworks as a way of showing that they'll always be friends.

Fighting Festival arc
Millianna along with Shou and Wally watched Erza's dance on Fantasia Parade.

Magic and Abilities
Nekousoku Tube: Millianna's only ability shown is her conjuring a magical rope in which she flings it at her target and binds them, effectively restraining them. Also, the magical rope constricts or stretches on command. The rope can also cancel the magic of the one it wraps around, in manner making Millianna an anti-mage, though never actually being stated out loud.

Trivia

 * In the extended version of Chapter 128, Millianna is seen alongside Wally and Shou as they watch the Fantasia Festival.
 * In the anime (episode 33), it seems that Wally has a crush on her.