So I'm taking some liberties on the Harry Potter lore by offering an explanation for how Salazar Slytherin learned Parceltongue to begin with. Hope that's okay with everyone.

Forty-Ninth Spell: Aruku

Haru checked Rui's nosy twin sisters Gaane and Fuyou to make they weren't listening in. Fortunately, they were too busy gossiping with each other.

"Do you remember when I passed out in Flying Class?" Haru quietly asked Rui.

"Yeah?" Rui said, looking perplexed.

"Well, I heard a voice say a name which made my chest hurt. Popuri-Dono thinks it was a reaction to someone trying to use kotodama to control me."

"Kotodama!" Rui exclaimed.

But realizing she spoke too loud, she checked to make sure her siblings didn't hear what she said.

"Is there something you'd like to share with the rest of us, Rui?" asked Peri, who was sitting at the head of the Byakko table as usual.

"Nothing, Big Sis," Rui said. Then she whispered to Haru, "I've heard kotodama is not an easy type of magic to learn. Maybe Warumo used it."

"That's what I think too. But I didn't succumb to it because my mother placed a magic seal on my chest where my birthmark is that's supposed to sense and repel evil."

"So Warumo touching you in the nightmare caused your mother's seal to react, just like it did in Flying Class. But why would a magical seal cause you to have chest pains and fainting spells?"

"Beats me. It could have something to do with that mark I'm supposed to have that you mentioned on the train, or me being an Aruku."

"Aruku?" Rui's eyes widened. "You think you're an Aruku? Do you know what that is?"

"No, I don't! Higa was about to explain it to me last night, but I got interrupted by Hikari showing up in the library."

"An Aruku is someone with the magical ability to talk to snakes. The English Wizards call such people Parcelmouths."

"That's it?" Haru chuckled. "Based on the way Higa reacted when I said that word, it sounded like a bad thing."

"Speaking to snakes isn't a common ability, and those who have it tend to be associated with Dark Wizards. For instance, Salazar Slytherin, one of the four founders for the Hogwarts School of Witchcraft and Wizardry in England, was said to speak Parceltongue. That's the language Parcelmouths use to communicate with snakes, which is said to sound like a series of hisses."

Haru then remembered when his adopted mother Papurika interrupted his talk with the tree python Moriko at the Kyoto Zoo, and how she claimed he was making a bunch of hissing noises. Even though from Haru's perspective, he was speaking to Moriko like she was talking to him using words and not hisses like Papurika claimed. This made him think back to all the times he spoke with Heshi in her serpent form, and a pit in his stomach began to grow.

"But according to an older legend, Salazar learned Parceltongue from Yamata no Orochi when he briefly traveled to Japan in the Middle Ages using the Dutch trade route," Rui continued, not noticing Haru's sullen face. "Then not long after, Orochimaru came along and he too talked to snakes making him the first documented 'Aruku'—which is also the name for the language he used for conversing with snakes. From that point on, anyone else who gained this power became collectively known as Arukus and were automatically suspected of being followers or descendants of Orochimaru."

"What are you saying?" Haru said, barely controlling his anger. "That I'm related to Orochimaru, because I speak the Aruku language?"

"No, but—

The familiar crowing sound rang through the Student Dining Hall, causing Haru and the other students taking summer classes to leave. But Haru couldn't bring himself to go to class, so he went outside and sat on the edge of the landing platform where the Ōkumo Storm Petrels landed and took off from.

"So when I thought I was speaking to snakes like people, I was actually speaking another language?" Haru shook his head. "I don't want to believe it. Warumo must have cursed me with the ability when I was a baby."

"You can't curse someone to become an Aruku," said a familiar voice behind Haru. "You're either born one, or you inherit the ability from someone else."

Haru looked up and saw Higa with a broom in his hand.

"I take it you found out what an Aruku is," Higa guessed as he used the broom to sweep the landing platform. "Sorry I didn't fill you in sooner."

"Why didn't you tell me I was one?" Haru demanded, looking away. "Because now in addition to being an Osozaki, I'm basically a freak among wizards!"

"Don't say that about yourself!"

Letting his broom go, Higa forced Haru to get up and look at him. "You're still Haru, even if you developed your magic powers late as an Osozaki or talk to snakes like an Aruku."

"How can I face my classmates now, though?" Haru complained. "If they think I'm somehow a distant relative of Orochimaru, they won't trust me anymore."

Higa's left eyebrow raised. "Are you sure? Rui and Hikari seem to trust you a lot. So do Nayu and Seita. You can't judge what they're going to do if you haven't told them anything yet."

"Well, Rui was the one who filled me in on what an Aruku is."

"And did she run away after telling you?"

"No."

"Then she clearly still trusts you. So I would go to her and apologize as soon as you can if I were you."

"What about everyone else?"

"You can choose to tell them if you want to, but I'm sure they won't judge you the way you're judging yourself right now. I know you're going through a lot with seeing Daichi and keeping up with schoolwork."

"I'm also having frequent chest pains and fainting because of this stupid seal my mom placed on me! Though I guess it's mainly because of Warumo using kotodama on me, which he tried to do again in a nightmare I just had."

Higa looked concerned. "If he was using kotodama, it might not have been a mere nightmare."

"What do you mean?"

"An experienced kotodama user can control someone from a distance by reaching out to the person in their mind."

"Like telepathy?"

"Something like that. And if Warumo is trying to use kotodama on you through your dreams, he's more powerful than I imagined."

"Is there anything we can do to stop it?"

"Possibly, but I must speak to Dōmeki-Sama before we try it."

"Why?"

"Because it will involved a great deal of pain—even more than what you've been experiencing lately."

To be continued…