Alicia Crystella is an Imperial Knight. She was born as a daughter of a duke house.
She is a tall, beautiful woman with a thin body and long, slender limbs. She also has long waist-length red hair.
She also wears small, edged glasses, which gives her an intellectual impression, along with wearing lightweight, easy-to-move-in armor, that lets her shoulders out, and a mantle. Her armor highlights her breasts.
Her public face is that of a kind, polite, friendly, and gentle person with a strong sense of moral justice towards anyone who threatens the peace and safety of the kingdom and its people along with having an amazing communication ability, which shows she has a sharp awareness of her surroundings and the people around her.
Her true self, on the other hand, is one who hates all the Races, including herself, calling them unsightly and weak, while she truly admires Demonic Beings, considering them beautiful and superior lifeforms.
However, both her public and true selves share one common trait. In both forms, Alicia was someone that was too serious. No matter what she did, she earnestly exerted her all without making any compromise. What she loves most about the Demonic Beings is the sheer amount of damage and destruction they do, with little to no restraint, and is enamored with Diablo for the same reason. The fact that Diablo calls himself "a demonic king from another world" only serves to amplify this mindset. She is obsessed with the principle that nothing should be left half-finished. She's really good at pretending to be a kind, sane woman. She's really sociopathic and hates everyone, including herself.
Her mother and father are abusive parents. They force her to study "proper" education until it damages her eyesight, then berate her for the glasses she wears so she can actually see (at least well enough to actually be able to recognize who she's talking to), routinely go through her possessions without notice or consent, despite her being a full-grown adult, and summarily destroy anything they consider "improper", only notifying her afterwards, and are constantly dismissive of her career and efforts, even going so far as to threaten her with ambushing her with a "proper" husband that they choose for her if she doesn't hurry up and find one for herself. She was forced into becoming an Imperial Knight, and endured a great deal of humiliation in the process, as a token female knight. Her hatred just kept on building over the years until she snapped, and wanted to end it all.
She is noble and strong since only those with a pedigree and true strength can become a state knight.
Her weapon of choice is a sword.
While she is well regarded by the King and publicly an state knight of high esteem, Alicia hates the Kingdom and its corrupt officials.
Alicia views Edelgard as a beautiful being since she is a Fallen, but is also loyal to her since she saved her life from the other Fallen that tried to kill her when their plan to fully awaken Klem failed.
She wanted to revive her in order to destroy the races but was disappointed that when she revived she had a childish mentality and was persuaded to not harm the races. She then conspired to awaken her with hatred by having Saddler harm someone Klem cared about.
When Alicia initially met Diablo, she merely thought of him as a strong being that could be manipulated into furthering her goals of reviving the Demon King and causing the destruction of the Races. After Alicia was attacked by the Demonic Beings other than Edelgard for failing to fully revive Krebskulm, she lost her purpose in life until Diablo gave her a new purpose. She is now fiercely loyal to Diablo. In exchange for Diablo and Krebskrum's aid in healing Edelgard, she first offers to take her own life, when Diablo prevents that, she willingly devotes her life to his service. It doesn't hurt that she interprets Diablo's words as seeking to root out and destroy the corruption of the kingdom she hates, even if it ultimately means overthrowing the kingdom in the process.