"They are delightful. In a very 'look at me twice and I'll dismember you' kind of way."
Astarion is one of the primary companions in Baldur's Gate III and is the designated rogue of the party. He is a high moon elf with pale skin, white curled hair, and dull red eyes. His shape language depends on the medium, as in the game is more lean and muscular, whereas in canon animated media he is a small, scrawny thing. Astarion was originally a magistrate who worked in Baldur's Gate and mingled with high society, but he was a crooked man, and was beaten near-death by those who disagreed with his rulings. He was 'saved' by a true vampire, Cazador, and became enslaved as his spawn. During this time, Astarion was a puppet for him to toy with, abuse, and intentionally starve. He was unable to deny any requests of his master, and was mainly sent out on the streets as a seducer, using his body to lure victims back to Cazador.

In the events of the game, Astarion was abducted by mindflayers, like the main character, and escaped the crashed ship. Dropped in the bright sunlight, he is immediately seen trying to cover his face, only to discover the sun is not burning him. Like the other survivors, he too had a tadpole parasite inserted into his brain, and its magic took away many of his vampiric weaknesses: sunlight and running water. While never addressed in-game, healing spells work on Astarion, which means his undead status had also been temporarily fixed by the parasite. All of these changes reverted at the end of the game (if he was not Ascended) when the parasites are killed, and Astarion is forced to retreat to the shade.

While not officially recognized, Astarion is likely on the asexual spectrum. Properly conveying any form of asexuality is rare in media, and even when done, people tend to overlook it entirely. Astarion is sex and touch-adverse, he does not want to be liked merely for appearances, and yet, a large chunk of the community inflicts those things onto him. This is fine, it is fictional after all, but whenever I (an asexual person) see someone understanding his asexuality, quite possibly their first introduction to such, always brings me joy.

"By the gods. I was afraid I was the only one. Ten years is a long time to be trapped in the hells without a kind word, or touch."
Karlach is sometimes the missed companion in the game, because the player can be persuaded to kill her, and because she is off the beaten path, unlike the others. She is introduced as a monster (devil) by Wyll, a veteran of the Blood War and a victim to the cruel machinations of Arch-Devil Zariel. She is the designated barbarian of the party. She is a tiefling with red skin, black hair with red highlights, large curled horns with one snapped off at the hilt, and flesh-coiled scars all across her upper body. Her shape language is consistent across all mediums; a tall, muscular woman. Roughly ten years before the game, Karlach worked for the post-Duke Gortash as a body guard, but the greedy man sold her to Zariel in exchange for an unknown reward. She was cast into Avernus and became Zariel's plaything, experimented upon with infernal machinery, resulting in her heart's inner functions to be replaced by a infernal engine. These changes give her an edge in physical endurance, and she can light her body on fire. She was set out on the battlefield as Zariel's champion, but she despised every minute of it.

In the events of the game, Karlach was abducted by mindflayers, like the main character, and escaped the crashed ship. When she did so, she was immediately chased down by Zariel's lackeys disguised as good-aligned paladins. She requests help killing these paladins, or at least, getting them off her back. She is over the moon when the player helps her, befriends her, and overall displays joyful, golden-retriever energy despite the horrors she has been through. She downplays her trauma, PTSD, but is grief-struck by the fact her infernal engine burns so hot she cannot touch anyone. This does eventually get solved, at the price the engine will burn itself out by the end of the game, taking her life with it.

From my perspective as someone with a chronic illness (one related to the heart), Karlach represents that to me. She is someone racing the clock and fighting the pain and grief her doomed heart creates, pushing through everything with joy and laughter, trying to set aside the inevitable. She finds small levities along the way that ease the pain, but they are all temporary. Especially near the end of the game, she mentions she is having trouble keeping up with the engine, feeling like it will blow - she stands there sweating, out of breath, begging to hurry up saving the world because she's not sure she'll make it that long. All she dreams of is living a full, normal life, but knows all she is afforded is a few short years fighting against her own body.