Mikasa and Levi are half siblings and Kenny is an uncle to them both. Mikasa's mother Carla had an affair with Kenny and as a result, Mikasa and Levi were born, however, their father is not confirmed. Kenny is not related to Mikasa and Levi by blood, but he protected their mother and them when they were young.
It is later revealed that Kenny was Levi's uncle, who took care of the latter after his mother, Kuchel Ackerman died. After teaching Levi how to fight, he abandoned him feeling that he could not be a good parent to Levi.
Levi and Mikasa also share remarkably similar personalities. They are both exceptionally loyal, apathetic, and reserved, only speaking when necessary. Levi shows the same loyalty to Erwin as Mikasa has to Eren. Beyond that, they both potentially share an uncle, Kenny Ackerman, also known as Kenny The Ripper.
He is the uncle of Levi Ackerman and brother of Kuchel Ackerman. He is a former serial killer from the Underground of Mitras and is a Captain of the Military Police Brigade serving in the First Interior Squad, the leader of the Anti-Personnel Control Squad and an enforcer of the Royal Government and the Reiss Family.
MIKASA AND LEVI ARE SECOND COUSINS.
No, Mikasa Ackerman is not related to either Levi Ackerman or Kenny Ackerman. While the three Ackerman family members are members of the same clan, they are not directly related. Levi and Kenny are from the same branch of the Ackerman family, while Mikasa is from a different branch.
In the case of Mikasa and Levi, they share the surname Ackerman. While there's no way they are siblings— they have different parents, after all— there's evidence that the two of them are distant cousins, especially when considering the power they share with Kenny.
Kuchel Ackermann (クシェル・アッカーマン Kusheru Akkāman?) was the younger sister of Kenny Ackermann and the mother of Levi Ackermann. She worked as a prostitute in the Underground.
In the 進撃の巨人 ANSWERS/Shingeki no Kyojin ANSWERS Guidebook, Hajime Isayama, the writer of the series, states that Kenny was attracted to Uri.
As it turns out, Levi's mother was Kenny's sister, who died when Levi was very young. As his only living family member, Kenny felt he owed it to his sister to look after her son, his nephew. Once Levi was able to fend for himself, Kenny felt he had fulfilled his obligation to his sister and left him.
Levi tells Kenny "My last name seems to be Ackermann, too," which suggests that it's something he heard rather than knew. He wouldn't use "seems" otherwise.
Rod Reiss - Though Kenny initially seemed loyal to Rod, acting as a sort of 'right-hand man' for him, he lacked any respect for the true King of the Walls. He saw Rod as a self-serving coward, incomparable to Uri at least, and only obeyed him to fulfill his dream of inheriting the Founding Titan.
Not much is really known about Annie after her defeat, she has cried twice throughout the series (the second time is a spoiler) but from what evidence we can gather is that she saw that her mission was a failure and was saddened by it.
Long after the persecution of the Ackerman clan, Kuchel took to working in a brothel in the Underground. She ended up being impregnated by one of her clients. Her elder brother Kenny Ackerman eventually found her, and unsuccessfully tried convincing her not to keep the child.
He refused to hold a grudge against Kenny, despite the latter's rudeness and repeated attempts to attack him; believing that because of the Reiss family, the Ackerman's hate was justified. He even went so far as to bow down to Kenny and formally apologize. He was also a very calm man.
Kenny Ackerman
If it weren't for Kenny, Levi would never have been strong, but that strength was eventually used against him. While Levi joined the Survey Corps, Kenny became the captain of the Anti-Personnel Control Squad. These two groups in the military ended up fighting against each other.
Almost all of the time, Kenny wears a hood that muffles his speech. Kenny being muffled is how he gets away with inappropriate and vulgar speech without having to be bleeped out or censored.
Annie Leonhart (アニ・レオンハート Ani Reonhāto?) is a graduate of the 104th Training Corps and former member of the Military Police Brigade.
"Normal Titan" (フツウノキョジン Futsū no Kyojin?) - The one Kenny gave to Levi and which was injected into Armin.
In some apocryphal texts such as the Testaments of the Twelve Patriarchs, and the Book of Jubilees, Levi's wife, his children's mother, is named as Milkah, a daughter of Aram.
Levi Ackerman (リヴァイ・アッカーマン Rivai Akkāman?), often formally referred to as Captain Levi (リヴァイ兵長 Rivai Heichō?), is the squad captain (兵士長 Heishichō?, lit. "leader of the soldiers") of the Special Operations Squad within the Survey Corps and is widely known as humanity's strongest soldier.
So according to the man himself, Levi did feel sadness and a sense of loss at the death of Kenny. Learning Kenny's identity, that he was his uncle and not his father, gave Levi relief. The question “who are you and what were you to my mother?” was something that had troubled Levi his entire life.
Petra Ral | Attack on Titan Wiki | Fandom.
Not only was Petra devoted to Captain Levi but he also hand-picked her to be in his special operations squad. Another point that showcased their potential was how her death seemed to affect the cool captain as it's later implied that Petra had feelings for him, making their pairing a tragic one.
No, Levi doesn't really have a love interest. Hajime Isayama (the creator) has said that Levi isn't the type of person to get into a relationship or have feelings for anybody.