TBHK with characters swapped

Hanako-san of the Toilet

Tsukasa was excited. "Did you hear the rumor? There are seven school mysteries. The most known one is mystery № 7. In the 3rd stall of the boys' bathroom in the old building, you can summon Hanako-san. She will grant you a wish, but you will have to pay a dear price."

"At this point we have to try that," Amane told to his twin brother Tsukasa. "Let's go and check if the rumor is true."

Amane knocked three times on the door of the stall and called her name, "Hanako-san, Hanako-san, are you there?" The door squeeked and opened, but noone was there.

"I'm here... behind you," the boys heard a strange voice.

A strange girl appeared to them floating above the ground, with light going through her. She had skulls on top of her school uniform, which was fitting. She had a seal on the cheek saying "seal". The rumors were correct: this was a ghost who was able to grant wishes.

"What wish brought you here?" asked Hanako-san. She was wearing high student uniform meaning she was a year or two older than the boys.

"W-we want for the boys from an upper class to stop bullying us," explained Amane. "They laugh at me for being such an astronomy geek and book worm."

"And they laugh at me for the interest in rumors and supernaturals," agreed Tsukasa. "But who's laughing now?"

"Two Yugi brothers," wrote down Hanako-san. "And your wish is to stop bullying."

"What kind of magic items you are going to use on bullies?" asked Tsukasa excited.

"And more importantly, is toilet involved in the ritual?" asked Amane with a smirk.

Slap!

"I do have something incredible here," Hanako-san gave boys a thin brochure on how to prevent bullying. "You see, if I am to use my magic powers, you will have a severe price to pay. For now, let's use this."

When angry brothers complained, Hanako-san had to admit that she in fact does not have a magic item that would help.

"Method №3," Hanako-san read from the book. "It is your emotional reaction that attracts bullies. If you pretend to not react, they will eventually go away."

The boys tried to do that next day, and it did not work at all. The bullies kept increasing pressure until Amane snapped. He had cried in front of bullies for the first time.

"Method №4. The bullies don't recognize you as people with feelings. Giving them a nice present will make them like you more."

"A nice present?" twins looked at each other. The next day, Amane brought a toy plane and Tsukasa prepared a lunch box. The plan backfired: bullies trampled over the plane and threw food at the brothers.

"Finally, method №10. Bullies only understand raw force. Stand your ground and punish them with their own means, and they will admit you as a superior." Yugi brothers were suspended for a week for causing a fight in the school yard. Worst thing, adults believed bullies and not twins.

"Your stupid plans don't work!" yelled Amane at Hanako-san. "We were suspended for doing it this way!"

"Well, I guess it can't be helped, since I'm newbie at such things," replied Hanako-san.

A newbie?!

"What's this, Hanako-san? You seemed to drop it," Tsukasa was holding a tiny bag with two silvery coins in it.

"It's mermaid armor— wait, Tsukasa-kun, don't eat it!"

Tsukasa quickly hid one of the coins in his mouth and threw the bag to the brother. Amane swallowed another.

"Tell us how to use them!"

"Alright, alright!" Hanako-san complied. "These things are mermaid scales. When two people ingest a mermaid scale, their body will become covered in steel like scales, but they will be bound to each other with a force beyond natural."

"What is this? What's happening?!" Amane was looking at his hands. They quickly became covered in fish scales. Then Amane disappeared. There was only a small fish blopping at the floor where he just stood.

"Quick! Find a jar and fill it with water!" Hanako-san yelled.

They placed fish Amane into the sink with water. Seeing what happened to Amane, Tsukasa spit out the scale he was holding in the mouth.

"You are very reckless, Amane-kun, you know it?" Hanako-san told him. "I tried my best to prevent this."

"What will happen to Amane now?" asked Tsukasa, "Will he turn back to human?"

Before Hanako could respond, they heard a loud crash, and a huge fish head emerged from the wall of the boys' toilet.

"This is mermaid," explained Hanako, "and she's here to retrieve her new servant. But I won't allow it."

Hanako-san pulled her hand beneath her school uniform and retrieved... a gardening shovel?

"Was she carrying it on her all the time?" wondered fish Amane. "How did it fit in there?"

"He is under my protection!" declared Hanako-san, "Get off of him or else!"

Hanako-san made a quick work of mermaid by banging her with the shovel. "Begone now!"

With the fight over, Hanako-san turned to fish Amane.

"Seeing as how I could not stop bullying, you still have one wish to fulfill. Do you want to become human again?" asked Hanako.

"Stop it!" interferred Tsukasa. "I see what you are doing. You did set this all up, did not you?"

"How could I?" asked Hanako-san surprised. "I did not call you, you came to me in the first place? I told you not to eat the mermaid scales, and he did it anyway?"

"It's okay, Tsukasa," they heard the voice of Amane, distored by water and bubbles. "I want to become human again. Please!"

"Alright then," announced Hanako-san. "I'll make you repay with your body!"

"Wait, what?"

Hanako-san swallowed the other mermaid scale. Amane went back to normal.

The price for the wish was for Amane to physically help Hanako-san. Turned out, Hanako-san was wanting a human assistant for some time. Amane was stuck on toilet washing duty for the days to come.