My beautiful sister-in-law who is only attached to me, and my childhood friend who just made her high school debut, barged into my house?

Following the sudden impulse that welled up in my heart, I ran along the familiar residential streets without pacing myself.

Even at the end of spring, the morning air was cool, which not only taking away the heat from my burning cheeks but also cooling down my head. Letting me reorganise my thoughts about Erika.

No matter how surprised I am about Erika not being my real sister, we’re still family living under the same roof.

I didn’t know what to do as my heart refused to listen to my mind.

I’m also a healthy young man.

When a girl as beautiful as Erika treats me so closely, it’s hard not to think about inappropriate things. Even more so now that I no longer have moral justification of her being my younger sister. No matter how much I think about it, my mind is a jumbled mess. I can’t seem to come up with an answer.

“Damn it, if this were Mio, I wouldn’t have to worry so much!”

I suddenly had that thought.

Mio and I have been together since we were children, we know each other’s good points and bad points, and we grew up together like brother and sister. I wouldn’t have been conscious of her as the opposite sex, worrying about making a mistake while living together.

“Fucking piece of shit teenage hormones.”

Shota continued to run, being swept away by his guilt and the wild thoughts that filled his head.

After running twice as far as usual, Shota walked to cool down, catching his breath, and then returning home.

His chest, which had been somewhat agitated, began to calm down. He slapped himself on the cheek and got back into the swing of things. Just down the street, he notices someone ringing the intercom in front of his house.

It was a strange girl.

She had bright, fluffy hair and was dressed in a fluttery, spring-like cherry blossom-coloured outfit. Her beauty was enough to make people’s jaw drop, so much so that she could be compared to Erika. In her hand was a rather large travel carry case, making her look rather incongruous.

Naturally, Shota had no idea who she was.

Could she be an acquaintance of Erika’s?

I don’t know, but either way, she seems to have business at our house.

“Um, do you need anything from us…?”

“……ah”

Shota spoke timidly towards the stranger.

She noticed me and made a puzzled face for a moment, staring me intently. Then she smiled wickedly.

‘Eh?’

At that moment, something caught my attention.

A strange sense of déjà vu hit me as a sneaking suspicion arose. As my eyes grew wider and wider, she jumped into my chest spouting bullshit in a theatrical tone.

“Sho-chan, I missed you!”

“Wait, wait, stop!”

“If I’m this nervous, Sho-chan might be able to hear my heart pounding.”

“Hey, what are you doing?”

“Oh my gosh, Sho-chan’s so flippant.”

“…who’s that girl?”

⁉

At that moment, Erika’s inorganic voice suddenly echoed from the entranceway. Her voice was so uncharacteristically emotionless and cold that it sent shivers down my spine.

Looking back timidly, Erika, who didn’t try to hide her displeasure, was looking down at us with a chilling gaze. I reflexively pulled the girl off and made up her excuse.

“Erika, this is…”

“Eri-chan!?”

“……?”

She then jumps onto Erika, squeezing her hand, looking Erika up and down, and chattering non-stop enthusiastically.

“You’re Eri-chan right!? Wow you’re such a beauty now.”

“Eh…huh?”

“Oh my God, your hair is so smooth and your waist is so thin! Your cheeks are also so squishy! I could get addicted to this!”

Erika was rubbed and being tossed around by the momentum of the girl. She looked at Shota, desperately signalling for help. Shota scratched his head and let out a big sigh.

To the girl whose appearance he didn’t recognize, but voice sounded familiar, he said with certainty

“Stop it, Mio. Erika feels uncomfortable.”

“Oh, I’m sorry. It’s been so long since I met Eri-chan, and she looks so different, so I got a little too carried away!”

“Mi-chan…?”

Erika’s eyes had a new spark in them as if her mood had made a full 180 reversal from before.

She was so different from the girl he had met just yesterday.

Ever since he was a child, he had thought he knew everything about Mio. But he didn’t know the girl in front of him.

‘Not even I recognized Mio earlier!’

Shota inwardly made such excuses to himself.

Then, with a dubious expression on his face, he decided to ask her directly.

“So, what’s with that look? Is it cosplay? It’s like you’re a different person.”

“Ah ha ha! It seems like not even Sho-chan could recognise me just now.”

“Ugh, let it go!”

“Hey, I told you I had something to do yesterday. My brother and father had made an appointment for me to get my hair and some other things done, since I’m going to be a high school student soon. Oh, this is what you call a high school debut!　How is it?”

Saying this, Mio spun around as if to show herself off. Her loose hair and skirt, which I had never seen her don before, fluttered and I couldn’t help but be dumbstruck by it.

I hurriedly avert my gaze and said bluntly, trying not to admit it.

“It’s not so bad.”

“Hmm, that’s it? I wish you would compliment me more.”

“Mii-chan, you’re so cute.”

“Thanks. I love how Eri-chan looks to. Sho-chan just isn’t honest with himself.”

“… What are you doing here, what is that baggage?

“Oh, those are my personal belongings. It’s heavy, so you carry it for me.”

“Hey, hey!”

As soon as she said that, Mio walked into the Katsuragi household as if she owned the place.

Although he was stunned, Shota hurriedly grabbed her luggage and followed her inside with Erika.

And the place Mio headed to was the room she should have been using as a storage room on the first floor.

Even so, the place was completely cleaned up, and desks, beds, shelves, etc. were brought in, and it looked like a normal room.

Mio looked around the room, murmured “Oh, nice” and turned around.

“Sho-chan, just leave my stuff around there somewhere. I’ll take care of the rest.”

“What? No, no, this is-”

“Hehe~ I’ll be living here with you from now on. Please take care of me.”

Mio showed a big smile like a flower blooming.

In contrast, Shota and Erika were stunned speechless.

They looked at each other, and as their slowly came to understand the situation, they exclaimed in surprise.

“WHAT THE FUCK!?”

It was a situation I couldn’t imagine even in my wildest dreams.

Mio is going to live in this house as well – the transformation in her appearance combined with the Erika situation, is making me feel unnerved. Erika, not knowing what to do, was at a loss as well.

In the midst of this, Mio clapped her hands as if she had come up with a good idea.

“Ah, that’s right! Since Eri-chan is here, let’s have play a game!”