Erika, with a mischievous smile, scoured her room for a pendulum. She knew very well that hypnotism needed a constant rhythm, and a pendulum would be the perfect tool.

After some intense searching, she finally found a small pocket watch that would do. She exhaled and held it high above her head, testing its rhythm.

Satisfied with her makeshift pendulum, Erika turned her attention to the real challenge. How would she calm her diligent and serious brother enough to hypnotize him?

She thought about Basch's hobbies. Military drills, document organization, cleaning weapons... Erika sighed. None of these activities were particularly calming.

Then, it struck her. The only time Basch truly relaxed was when he read. But how could she get him to read while swinging a pendulum in front of his eyes?

"A story. I'll tell him a story," Erika decided, clasping her hands in excitement. She then proceeded to scribble down a simple plot to keep Basch's attention.

With a plan in mind, Erika made her way towards Basch. He was in his office, hunched over some documents, scribbling notes in the margins.

"Basch," Erika said, trying to sound nonchalant, "Would you like to hear a story?" She asked. He looked up at her in surprise but agreed, nonetheless.

Erika began her tale about a brave knight and a trapped princess. As she wove her words, she subtly brought out the pocket watch, beginning to swing it.

Basch watched the moving pendulum, his eyes following the rhythm. His eyebrows knitted, but he continued to listen, not aware of Erika's true intentions.

As Erika’s story continued, Basch’s attention shifted from the papers on his desk to the swinging pendulum, and his eyes gradually became heavier.

Erika watched as Basch's features relaxed. His eyelids drooped, and she knew it was time. In a hypnotic tone, she said, "You are now a cat, Basch."

Basch seemed to stir, but he didn't protest. Instead, he gave a low, drawn-out yawn, not unlike what a satisfied cat might do.

Erika held her breath as Basch sat up, looking around with wide eyes. He then stretched, arching his body like a cat after a long nap.

Overjoyed and a little bewildered by her success, Erika watched as Basch continued to display cat-like behavior, swatting at an imaginary object in the air.

The rest of the day was amusing for Erika. She watched Basch stalk invisible prey, climb up on furniture, and even attempt to fit himself in a box.

He would occasionally look at her and give a small 'meow.' Erika found this both endearing and hilarious, unable to contain her laughter.

Erika provided him with a ball of yarn, which he batted around merrily. He even curled up on his chair, purring as he slept.

However, by dinner time, Erika started worrying about the length of Basch's trance. She had enjoyed the harmless fun, but it was time for him to return to normal.

She gently woke him up, swinging the pendulum again and saying, "You are Basch, not a cat. Wake up, Basch." But, he yawned and meowed softly.

Erika panicked a little but continued to try to awaken Basch from his feline trance. Eventually, after some effort, he blinked and sat upright, looking confused.

"Erika? What happened?" Basch asked, his voice full of confusion. Erika sighed in relief, "You were sleeping, Basch. You must've dreamt something funny."

Though he was a bit puzzled, Basch believed her. He returned to his routine, unaware that he'd spent the entire day being a cat.

Erika retired to her room that night, her heart thumping with the thrill of her achievement. She put the pocket watch away, thinking about her exciting day.

Although she was glad that everything was back to normal, Erika had to admit she'd enjoyed her day with the cat-version Basch. She fell asleep with a smile on her face.

The following day, Erika noticed Basch staring at a balled-up paper, curiosity in his eyes. He pounced on it suddenly, remnant of the feline behavior.

Basch looked surprised at his own action, looking up to see Erika trying to hold back her laughter. He just shrugged and said, "Must've been a funny dream, indeed."

Erika just nodded, agreeing with him. She then went to make some tea, leaving Basch to his peculiarities, a secret smile playing on her lips.

As the day ended, Erika looked at Basch working diligently at his desk again. Maybe, she thought, wouldn't it be fun to make Basch believe he's a dog next time?

Deep down, Erika knew the risk and chaos that might ensue. Still, the idea left a sense of excitement and anticipation. After all, everyone needs a bit of adventure, right?

And so, life went on normally in their little home. But in Erika's mind, the possibilities were endless. The memory of Cat-Basch would always bring a chuckle, as new plans brewed.

Hypnotism might have been a peculiar hobby, but for Erika, it was a treasure chest of fun, a secret she shared with her unsuspecting brother. Indeed, it was an unusual bond they had.

And for Basch, who was blissfully unaware of his sister's mischievous ways, life continued in its own rhythm. But every now and then, a sense of feline curiosity would spark within him.

It was a strange yet endearing household, filled with heartwarming love, innocent secrets, and hilarious, unconventional moments. A tale they would carry with them forever.

So, in the Hetalia world, our dear Erika and Basch graced every day with a new adventure, one pendulum swing at a time. What a peculiar, delightful pair they were!