I'll Cherish This For The Rest Of My Life (一生大事にします) is the first episode of the spin-off anime series Mahouka Koukou no Yuutousei. This spin-off follows the events of the main series from the perspective of the girls, especially that of Shiba Miyuki.
March 25th, 2095. To celebrate her 15th birthday, Shiba Miyuki goes shopping with her older brother Shiba Tatsuya in Yokohama. Miyuki enjoys her time with Tatsuya as if they are on a date, and she is ecstatic when he gives her a surprise gift. However, they are interrupted by a call from the main branch of their family, the Yotsuba, who are members of the Ten Master Clans. They ask Tatsuya to attend to an urgent matter. While Miyuki waits for Tatsuya to return, the fire alarm in the building goes off. Miyuki senses that this is a criminal act committed by someone using magic and heads toward the fire.
People are fleeing from a fire in a mall. Someone knocks into a child but Shiba Miyuki catches her and directs the little girls brother take her to the exit before running towards the fire, her fate as a magician.
At home, Tatsuya is calibrating Miyuki’s CAD. Miyuki is only wearing her underwear, but Tatsuya does not seem to notice which makes her feel insecure. Tatsuya brings up her upcoming birthday and asks what she wants. Miyuki then decided to ask him to spend the day with her as her present.
The siblings head out on a shopping trip and Miyuki is elated. Noticing the couples around, Miyuki tries to hold his hand but gets embarrassed. Tatsuya notices and takes her hand, and she is reminded they are siblings and laments to herself that wanting more would be unreasonable. They continue shopping eventually going to a clothing store. Miyuki tries on a swimsuit and showed it to Tatsuya. Tatsuya points out that it suits her but she isn't appropriate in the current setting, embarrassing her.
The siblings stop for lunch at a café and Tatsuya surprises Miyuki with a birthday special spread. Miyuki inadvertently draws a lot of attention, and when the staff realise that she is responsible for the extra business, the manager sends a free ice cream for the pair, mistaking them for a couple. Although Tatsuya tried to reject the offer but Miyuki is very pleased that they were mistaken for a couple and told Tatsuya it was only polite to accept and so the pair stay for dessert.
Continuing the date, the pair head off and Tatsuya stops by a shop window. Miyuki tries to ascertain why and when Tatsuya tries to ask if she would come inside the shop, Miyuki mistakes it for a kiss and tries to let him kiss her, until Tatsuya gets her attention and corrects the misunderstanding, though oblivious to it himself. They head inside and Tatsuya picks out a hairclip in an icicle design for her and buys it as her present.
The pair begin to continue their date when Tatsuya gets a call from the Yotsuba and has to head to the Magic Association, asking Miyuki to wait for him there. While she waits, Miyuki laments their situation.
At the association, Tatsuya meets with Hayama Tadanori who gives him his mission, to deal with a rogue enhanced magician, explaining he is there to clean up due to the political issues related to the case. Tatsuya asks the target’s location, and Hayama tells him he is here, targeting the Magic Association. Hearing this, Tatsuya rushes off to Miyuki.
Back in the mall, Miyuki realises the fire is unnatural and magic is involved and rushes to intervene. Arriving to see Tatsuya’s target engaging in arson, Miyuki is angered by his misuse of magic and uses her own magic to put out the flames. The pyromaniac is enraged and pulls out his CAD but before Miyuki can act, a little girl wonders into the fray. Miyuki moves to protect the little girl, losing Tatsuya’s present in the process. Absolutely enraged, Miyuki closes in and overpowers the pyromaniac with magic, freezing him solid. Tatsuya then arrives, the little girl on his back, and grabs Miyuki and has her run from the scene as she used too much power. As they flee Tatsuya tells her he took out the surveillance and as it has Tatsuya’s target, Hayama will deal with covering up her involvement.
Outside, the siblings reunite the little girl with her mother. Realising she lost the present, Miyuki is about to run back inside, but Tatsuya has already collected and restored it for her, much to Miyuki’s elation.
Later, Hayama reports to Yotsuba Maya the success of the mission and explains the pyromaniac was working in collusion with a co-conspirator, the anti-magic organisation Blanche. Hayama reports the matter was handled quickly by Tatsuya. Maya comments she feels Miyuki did most of the work but will not object, given the result. Ordering Hayama to ensure Miyuki’s identity is not compromised. Maya comments she will not admonish Miyuki this time but will do so if Miyuki is not more careful.
At home, Miyuki tries on her new uniform.
At First High, Saegusa Mayumi has recognised Miyuki from the very blurry footage of the incident which survived, matching the picture with her student ID photo. Mayumi is reassured to have such a capable girl enrolling and confirms that she will be recruiting Miyuki to the Student Council. Watanabe Mari is disappointed that she cannot recruit Miyuki for the Public Morals Committee, to which Mayumi comments that there is another one, a boy, enrolling and decides Mari to target him (Tatsuya) instead.
- The episode's title is Miyuki's response to Tatsuya after giving her the hair clip a second time and true to her word, she is always seen wearing the hair clip.
- Miyuki's ending speech on the episode is also the opening speech she made on Enrollment Chapter I (Anime).