The concept of Ackerbond is one of the most controversial theories present in the Attack on Titan community. The theories are diverse as they range from believing an Ackerbond is a cruel notion designed to control Ackermans to insisting there is no bond between the pairs.
However, if we disregard the existence of such a bond, then there are some moments in the series which suggest Mikasa’s deteriorated health. Her comrades decide to overlook those subtle symptoms since she is an Ackerman and is considered to be one of the strongest races.
Could Mikasa have been really sick throughout the entire plot without anyone noticing?
While arguing with Armin and Mikasa, the protagonist of Attack on Titan goes on to explain that the Ackerman clan was designed to protect the King. Eren goes as far as to label them as a byproduct of experiments undertaken by Eldia on Ymir’s subjects. He furthermore added that their motive was to produce a bloodline capable of holding the strength of a Titan in human form. Ackerman still has the instinctual traces of this, which raises an urge to protect their host from any kind of danger.
Eren even recalls when he commanded Mikasa to fight the kidnappers when they were young. He tells her that this command activated Mikasa’s instincts, with her mistaking Eren for the host she was designed to protect and sacrificing her free will. According to him, this is the only reason Mikasa cares so deeply.
How was the Ackerbond between Mikasa and Eren Jaeger?
According to the information we have from the anime and the manga, the Ackerbond is considered a connection that ties an Ackerman to a Royal Family member, making them completely submissive to and overprotective of them. However, this turned out to be false. Eren just made up this story to keep Mikasa away from him and even refuted by Zeke, who inherited the knowledge of Tom Ksaver, who had done multiple research on the lineage of Ymir.
However, if this doesn’t exist, it simply implies that Mikasa’s getting headaches or light-headedness was a symptom of some underlying illness. A fan theory suggests this fact and furthermore explains that no one brings out the subject because she’s the second strongest character. There have been scenes that presented her with spontaneous headaches along with her body feeling weak. She has been shown spacing out in the jail scene in season 3 and the Jeagerist headquarters. Even Eren states she has gotten too thin and needs to care for herself.