~ About 8 years ago, during the winter months

'Tenri~!　Let's get going!
'Wait, there's no need to be in such a hurry!

　One day in the evening, two girls were chatting on their way home from school.

　One of them - Nantenashi, ever since she could remember, had a family that could be described as one and the same.
　It's the same with her younger sister, who is a twin, so she's a perfect match, but her personality is the opposite - Minami Yuna.

　It's not just the fact that the person you are looking for is a very serious person, but also the fact that Yuna is an active girl, and the difference is so great that it's easy to distinguish her from someone else, except when you meet her for the first time.
　But that doesn't mean they don't get along, and even in their third year of high school, the two are still very close.

'Because you want to be with the person you love, even if it's just for a second longer, right?'
'Certainly in general, and I'm sure the two of you would be a good match, but he's also my tutor, in case you're wondering.　I don't want you to flirt with me too much beside me...
'Then why don't you get a boyfriend soon, Amani?
'Don't say it so easily...'

　In response to Yuna's light-hearted tone, Tenri muttered in dismay.

　Yuna had a man she was in a relationship with, and Tenri knew him well.
　Moreover, it was also the reason why the two of them would be hurrying home from now on.

　In the meantime, they arrived at home, opened the door and went in.　

''Tadaima!''
I'm home.
Welcome home - Yuna, Tenri.

　When the two daughters returned home, their mother - Mayumi - welcomed them with open arms.

'The doctor is already here.
Wow, I knew it!　Amani, hurry up, hurry up!
Oh, God!　Please line up your shoes properly!

　Knowing that the person she's looking for is already waiting for her, Yuna goes to the back room at once.
　Tenri rushes after her.

　One man was sitting in the room that wasn't their own room, the one used for classes with the tutor.

　He had light brown hair, bright green eyes reminiscent of emeralds, and black bruised glasses that gave him a mild impression.

'Hello, both of you.'
'Hello, sir!　I've missed you so much!
Yuna!　Don't try to hug me too soon when I haven't even started studying!
'Hahaha...'

　In order to make sure that Tenashi and Yuna take their high school exams, her parents hired a tutor - Tatsuto Manaka, who would later become Tenna's father.
　In addition, Yuna, who became involved with him when he was taking the entrance exam for high school, confessed her feelings to him when he announced his acceptance, and they had been dating ever since, so he was like family to Tenashi.

'I'm sorry, Tatsuto-san. No matter how much you're my girlfriend, Yuna is causing me trouble...
I don't mind. It's that positive attitude that attracted me, so I'm just grateful that you've been so patient with me, Amari.
'Well, if you're going to be my brother-in-law eventually, it would be helpful if you could be a little more modest.
'Oh, hahaha...'

　Tatsunin, who is supposed to be a good enough adult, is overwhelmed by his sister-in-law, who tells him she wants him to get his act together.

　Anyway, when Watahira finds out that Yuna and Tatsunin have started dating, the father-to-be is very upset.
　The age difference between the two is six years, Yuna was still in high school and Tatsunto was about to graduate from college, so the problems piled up between them are hard to ignore, even without the hassle of dealing with a foolish parent.

　In fact, Watahira had given him a hard time for breaking up with him so many times that he almost forced Tatsuhito to quit his job as a tutor.

　Nevertheless, the two vowed to continue their relationship.
　Up until now, he's been earning money by working as a part-time tutor and cramming tutor, but he's passed the exam to become a teacher at a public high school, and he'll be able to start teaching next year, so he won't be lacking in income.

　As for Yuna, Tenashi had heard that she was planning to get married upon graduation from high school, so it was only a matter of time before Tatsunin became her brother-in-law at the earliest.
　Even his father, that idiot of a father, had approved of the marriage.

''You're the one who should tell Tenri~. He's so beautiful like me, but he doesn't have a single flirtatious story to tell!　I don't want my sister to go back to school late or anything...
Yuna~...?
'Hee!　Gosh, I'm sorry!

　Since they are twins, Tenri and Yuna have good looks without an inch of difference in their faces, and they were even rumored to be two great angels at the time.
　Yuna already had a boyfriend, Tatsuhito, so even though she may have attracted attention, she didn't make advances to him early on, but Amari, who didn't even have her own love interest yet, was being pushed around like a horde of people.

　But the real Amari cut them all off.

''How should I put it.......it's because I don't have anyone I'm on the same page with like you, Tatsunin-san.
What?　So Amari had a hobby that involved sleeping with her sister's boyfriend?
'Hey I don't have such a harried and unpleasant hobby!　I think you're a good person, Mr. Tatsunin, but only as family!　Even I'm worried that I'm not ready for my first love in my senior year of high school!
'Well, well. We're twins, but we have different romantic values...

　As if to say that if you hit it, it will resonate, Tatsunin stops Tenri from going along with Yuna's mischievous words and actions every time.

　Anyway, when it was time for study in moderation, the two of them showed amazing concentration and devoted themselves to it.
　Yuna, who tends to be seen as being bad at studying by nature, works diligently in this aspect, just like Amari's twin sister.

　So after concentrating for about two hours, I finished today's class.

I'm so tired~!　Sensei~ Chu and share your energy~
'Yuna you were so adamant about not making out when I'm around...'
''It's embarrassing to kiss in the presence of Amari-chan...''
Mmm~....

　Yuna casually begged for a kiss while standing tall, and was accused by Tenashi and Tatsuto, albeit in a different vector.
　After being told by her lover, Yuna couldn't help but puff out her cheeks and reluctantly agree.　

''For now, my mother has asked me to join her for dinner as well, so would you like to join us, Tatsuto-san?''
Thank you.
'Yay!　You and your teacher...

　The moment Yuna stood up vigorously with glee because Tatsujin was also with her for dinner, her face suddenly turned pale and she started to suppress her mouth with both hands.
　That sudden change, which was not just a matter of time, made Amari and Tatsujin unable to hide their confusion.　

''Yuna!
And take him to the bathroom!
Yes!

　On the spur of the moment, Tenri runs to the toilet and rubs Yuna's back with a grim expression as she gapes at the toilet bowl.
　There is no indication that Yuna has a pre-existing condition from birth.
　But the fact that the situation happened in spite of that, Tenri couldn't help but wonder what had happened to her sister.

　After that, she calmed down, and Tatsuhito heard the commotion and gave an explanation to Mayumi.
　Then Mayumi finished listening to the situation and faced Yuna with a face that didn't allow any jokes.

　Since she is usually so carefree, both Tenashi and Yuna are nervous and prepared in an unusually serious atmosphere.

''........Mom?''
Yuna. Be honest.
...what?

　Amidst the swordswept air, Mayumi asks her daughter one thing.
　That is..........

"──the most important thing is that the reason for the coming of the most important thing is........?
Huh!
What...?

　It was about the inevitable physiological phenomena of women's lives.
　Yuna's shoulders trembled a little, and Amari was astonished to find out what the question was about.

　It wasn't just the two of them, but also Tatsuto as well.

''About two months ago, but........''
Yeah.

　In response to Yuna, who replied while stumbling, Mayumi only quietly lowered her eyes.

　Amari and Tatsuto, who were listening to the conversation up close, were speechless with surprise.
　That's no wonder, there's only one reason why Yuna's body, which is supposed to be in good health, doesn't have a menstruation....

　The only reason is that Yuna is pregnant.