Leanne

Leanne is former member of the hero party until it was disbanded due to Arios losing his status as a hero for his betrayal.

She was betrayed by both Arios and Monica for being useless to them, as well as being demonized by Monica. She was killed by Rein (unwillingly) to put Leanne out of her misery. After her death, Leanne was later buried by both Rein and his companions.

Her death (along with Aggath's demise) had caused Mina to betray Arios and intend to form an alliance with Rein after she realized how evil he truly was where she also died at Arios' hands. Luckily, Leanne (as well Aggath and Mina) was later avenged when Rein finally killed Arios for his betrayal and delusions.

Appearance
Leanne is usually seen in a mage outfit with her long purple hair. She wears a large hat that resembles a witch’s hat.

After being demonized by Monica Eclair (who was ordered by Arios of betraying her), Leanne became monstrous until she reverted back into her original form after Rein killed her.

Personality
She is haughty and arrogant and like the others looked down at Rein. But she still admitted that Rein's skill of taming Strongest Races was impressive going as far to apologize to him when she accepted her defeat at his hands (unlike Arios who refused to accept his defeat).

She was shown to be devastated when Arios betrayed her and the other Heroes but still sided with him. Like Aggus and Mina, Leanne now had hatred towards Arios for his betrayal and after he allowed Monica to betray Leanne without a second thought where Leanne was turned into a demon by Monica and killed by Rein and his companions.

After becoming a demon due to both Arios and Monica's betrayal towards her for being useless to them, Leanne became a mindless monster causing her to lose control of herself and struggled with her new transformation, until Rein and his companions decided to put Leanne out of her misery and freed Leanne when Rein (unintentionally) killed her after Shroud failed to try and convince Leanne that Arios was only using her as a pawn all this time and the fact that there wasn’t a way to change Leanne back.

Abilities
Leanne was an accomplished wizard indeed. She was able to cast a large amount of spells which put her way above the average wizard, but much like the other members of the hero party, her skills, for which she called herself the strongest magician in the world, were immediately proved to be inferior when she it was revealed that she only learned weak spells and was not even close to those of Tania, whose magic was so much stronger than Leanne's that she not only managed to effortlessly nullifying every one of Leanne's weak spells, but then managed to fool her by casting a powerful spell through which Leanne, along with Mina, were left completely helpless.

After she was demonized by Monica (who disposed of her under Arios' order), Leanne gained superhuman strength and caused Rein to struggle. But she was nonetheless killed by Rein (which was unwillingly and unintentionally).

Trivia

 * Currently, Leanne is the only former party member and friend that was killed by Rein (though it was unintentionally).