WARNING: The following contains spoilers for The Irregular at Magic High School, "Reminiscence Arc," now streaming on Funimation and Crunchyroll.
Magic is a force that exists in the world of The Irregular at Magic High School, but only a small handful of people are capable of using it to manipulate matter as magicians. While magic is something a person has to be born with, people can also become augmented magicians through gene manipulation and a magic equation. One such character is Minami Sakurai, who is a second-generation augmented magician of the Sakura series. She's also related to a first-generation augmented magician named Honami Sakurai.
While Honami only appears in the "Reminiscence Arc" of The Irregular at Magic High School, she's still an important character whose actions during the events of this story helped shape the present timeline of the series. In addition to having an important role in a major battle, she's also the character who raises important questions about the status quo of augmented magicians that nearly parallels that of the replicants from the Blade Runner franchise. Despite being a supporting character, she is the emotional core of the story.
Honami is introduced in "Reminiscence Arc" as the bodyguard of Miya Yotsuba, who was the leader of the Yotsuba Clan at the time. While Miya is vacationing in Okinawa with her daughter Miyuki and her son Tatsuya (who is also treated like a bodyguard), Honami serves similar functions to her niece in the present and uses a lot of the same powers. Like Minami, Honami also takes care of housekeeping duties, escorts Miya and her children to various places and shields them from danger. While Honami is loyal to her owner and Miya does in fact treat her with kindness, Honami is also aware of the fact that she is no different from a slave.
After she escorts Miyuki and Tatsuya to a car on their way to a dinner party, Honami gets a moment to herself to not only think about her place in the world, but also that of Tatsuya's, whom she can relate to. Despite Tatsuya being a member of the Yotsuba Clan by blood, the fact he was born "a deficient magician" -- per his mother's words -- caused him to be downgraded to a similar status to Honami herself, which she thinks is wrong. Although Honami is completely unaware at this point that Tatsuya also had his powers augmented by his mother and aunt when he was younger, Honami is still right to be horrified by his dehumanization.
When Honami learns the truth about Tatsuya's powers, she decides to go to his aid during an attack on Okinawa by the Great Asian Union. Not only does she risk further shortening her lifespan to ensure victory to both Tatsuya and the Okinawa Naval Base, but she even implies that she wants to bring about her own demise. She ends up confirming this when Tatsuya attempts to save her life a second time (having resurrected her during an earlier attack) and she stops him from doing so. When explaining her decision, Honami confides the truth about her existence to Tatsuya.
Beginning with the fact she was bought by the Yotsuba Clan before she was even born, Honami has always been aware of the fact she would never have control of her own life. As an augmented magician who was bioengineered with a very short lifespan to serve Miya Yotsuba, she was robbed of many life experiences others get to enjoy, and something about that made her profoundly unhappy. Rather than continue existing as an instrument for someone else's use, Honami rationalized that if she couldn't have control over her own life, then she wanted to at least control her own death.
Specifically, Honami wanted to die as a human being who made a heroic decision that was not informed by her sense of duty to someone else. She wanted to go down fighting for what she believed in and to have her wishes honored like any other human. In addition to being memorialized, Honami requested to have her cremated remains scattered in the ocean as a final symbol of freedom.
