I, who had succeeded to stop the young lady's weapon creation that took the name of an obento, am currently inside the carriage and on my way home.

The servants of the Frontier Count's Household sent me off while shedding tears of joy, and the young lady also gave her consent that she won't do it again.

My master was displeased for some reason, saying 'To make advances at a girl in front of her father, you sure are a lady killer.' but when I answered 'Then, do you wanna eat that again?' he seemed to grow silent.

Honestly, you're so troublesome.

However, with this the crisis has passed.

All that's left now is to keep training hard and keep acquainted with the nobles.

In one year I'll marry the young lady and then there's the invasion of the neighboring country.

In order to do that, I must keep trying my best......

I am now the adopted son and the successor of the Knights Division Commander.

An ordinary person who came from a different world has become a noble, huh? Moreover, if everything goes as planned, I'll be getting married with the young lady of the Frontier Count's Household, huh.....?

A son-in-law, huh.......? Will I be living together with that old man?

Ha ha, my tears won't stop falling.

I felt a tingling in my arms and then they grew numb.

Oops, I completely forgot about it......This book that the young lady entrusted me with.

It's a heavy, massive book with extravagant black leather covers and beautiful golden designs.

There's the Frontier Count's Household family crest imprinted on the front cover, a shining large snake coiling around a shield.

"An exchange diary, you say?"

Yes, no matter how you look at it, this book seems to be filled with dark magic prohibited spells....this is the exchange diary that the young lady gave me.

It was prepared by my master for when I managed to stop the weapon creation.

I really wanted to turn him down, but since both my master and the old Frontier Count, who showed up before I could even realize, insisted that I accept it, so I virtually couldn't refuse anymore.....

With a twitching face and a trembling body, I moved to grab it, but the young lady approached from the side with a terrible speed and stole the book before I could even touch it.

After she finished writing today's share, she returned this prohibited book to me by throwing it inside the carriage.

Since I arrived at my mansion, I decided I would have to deal with this dark magic grimoire as soon as possible.

Maybe I'll just write something casually while sipping some of the tea that was already prepared for me in my room.

For today, I wrote something like 'I'm happy we started this exchange diary. I really like you, young lady.'

Since it's the first day, she also wrote something similar, so it shouldn't be any problem.

I will send it to her tomorrow morning, she'll write something in the evening and sent it to me the following morning; and we'll probably stick to this schedule.

"However......the dark magic's influence is already astounding........"

That's right.........

'I'm looking forward to this exchange diary that we started today!'

With only this little sentence, the diary was emanating an overwhelming magical power.

It's supposed to be a happy feeling, but the fact that she wrote it negatively sent shivers down my spine.

That's why I didn't want to do it......

Damn it! But well, since both my master and the Frontier Count are indebted to me now, I can't help but accept my fate.......

Because leaving this grimoire as it is might turn out to be quite dangerous, I must do something about it.

I asked the maids to bring me some mithril, and I made a chain in order to seal the black magic. I secured it with a mithril padlock as well.

Since this metal called mithril has a high affinity for magic, even though it's rather expensive, it is extensively used.

It's such a waste of my light magic, but it can't be helped.

If I don't do this much, the servants who deliver the book might just drop dead.

It's completed......The extravagant, black leathered book is now sealed with a chain.

...............Exchange diary? No, this is definitely a grimoire, a prohibited book!

How should I explain this to the young lady though?.......I probably can't tell her honestly that......it's because of her dark magic.

It seems she had some traumatic experiences.

Let's go with this then!

I quickly wrote a letter and added the padlock key in the envelope.

Since I already went through all this trouble, I also made a set of fine keys, and I hanged mine around the neck.

Naturally, they're also mithril-made.

I gave the grimoire and the letter to a maid and I instructed her to run an errand for me the next day.

If I forget to send it in the morning, it might turn into something quite nasty.

It should be okay now. Today was a really awful day.

~ The following day at the Frontier Count's Household ~

A major incident.....The servants were making an uproar over the exchange diary that Zest-sama has sent.

The exchange diary that the young lady was so excited about was sealed with a chain.

Was this interpreted as a declaration of not wanting to continue with this exchange diary, I wonder?

How sad will the young lady be once she sees this?

Some of them had pale faces, some of them broke down crying; the Frontier Count's Household was facing yet another crisis.

And then, the young lady showed up.

"What's with this uproar so early in the morning? Is it that 'it' has already arrived?"

They could no longer hide it from her.......The maids timidly handed over the exchange diary.

Her mouth twitched for a moment.

"........I.....I will be in my room for......a while. Make sure no one disturbs me."

She said that and left.

The servants that were left behind were standing stock still......for like forever.....

She returned to her room and opened the letter while trembling.

Why was the exchange diary sealed? Did he hate it that much?

She started reading while cladding her body in a gloomy lair of dark magic.

A far away scream could be heard, it seems that someone might have collapsed, but for now the letter was more important.

'－To my lovely fiancée －

I know that you'll be shocked to see the exchange diary in such a condition, but I intend to explain it properly, so please calm down and continue reading, okay?

To be honest, I'm a very jealous person. What if someone else gets a glimpse at what you wrote in this diary?......When I thought about this, I couldn't bear it.

That's why I made sure to seal this diary so that no one can have a look at it without using the key.

I want to know more about you, but I don't want others to have the same privilege. Please forgive my selfishness of wanting to monopolize you......

I enclosed a key for you in this letter and I also attached it to a pendant so that it would be easily worn as a necklace.

While thinking of you, I embedded it with defense magic so that it could protect you in my place when I'm not around, so promise me you'll always wear it on you.

It's mithril-made and it's filled with light magic and all my love for you, therefore it will neither rust, nor rot.

It will be eternally unaffected, just like my feelings for you.

While using these keys, let's enjoy this exchange diary from now on! Please!

－Your selfish fiancé －'

"It can't be helped. Really now, you're such a selfish person!"

That day, the young lady was clad in a fierce and wicked magical power that no one has ever seen before, all while constantly paying undue attention to the necklace at her chest.

The servants filled me in with the details the next morning, all while looking completely devoid of life.