Back in Time, to save our teacher( assassination classroom fanfic)

Don't be Suspicious

Karma confidently sauntered to the back of the class. His pose was relaxed and with his hands stuffed in his pockets, Nagisa almost felt as though this was the old Karma. But, with further inspection, Nagisa could easily make out something off. His eyes, which used to be almost always half closed, were now sharp, calculating. While Nagisa wasn't worried about any of the other students noticing, he knew Karasuma- sensei, and most probably Koro-sensei would notice. Probably even Irina-Sensei. He might have to alert Karma later. 

Nagisa felt someone glancing at him. Turning his head slightly, he noticed Kayano steadily boring her eyes into the back of his head.  As soon as she saw him noticing her, she jumped a bit in her seat. He gave her a soft smile, which she returned, albeit hesitantly. 

Tearing his eyes of her and back to Koro-sensei's board he mentally listed the reasons as to why Kayano was staring at him. One, he was acting suspicious, two, he startled at her name, three, he was acting suspicious, four, he probably hadn't answered any of her messages that weekend, five, he was acting suspicious. So all in all, he was not acting like 'himself'. Plus, he added, her tentacles were still attached at that time. Maybe they were also adding to her suspicions. If that was true then maybe, even Koro-sensei's were alerting him. Nagisa winced at that. He really needed Koro-sensei to trust him.

"Well, Nagisa-kun, if you are so intent on day dreaming in my classes, you should come late as well."

Nagisa forced his body not to startle. He gazed up at Koro-sensei's ever smiling face, and gave him his best apologetic smile. He knew it would work. After all he learnt it from Irina-sensei and she got away with everything. 

"Gomen'nasai, Koro-sensei," Nagisa said bowing his head in a show of respect. 

Koro-sensei stared at him for a moment, before zooming back to the board. 

"Well if you can answer this question properly, I'll let you off scot-free."

Nagisa glanced at the board. The question was fairly simple. It was based on the The Prime Number Theorem. Then it struck Nagisa. He hadn't done this problem up until college. And even then it was Karasuma who had taught it to him. It was a spies secret code. Dammit! That meant that Koro-sensei was extremely suspicions of Nagisa. Nagisa carefully schooled his features to one of pure confusion. 

"Gomen'nasai, Koro-sensei," Nagisa repeated, bowing his head. "I honestly do not know the answer to that one."

If it could, Koro-sensei's smile got wider. 

He faked a sigh," Very well, Nagisa. Just meet up with me after school today. I want to go over this with you." 

Nagisa nodded. While sitting back down he glanced at Karma, who gave him a nod. Nagisa hoped it was of approval. It would suck if it wasn't. He was already feeling guilty, about the 'thing'. He tried paying attention to the rest of the class, but he just couldn't. His mind was whirling. What did Koro-sensei want to talk about? Was Karma mad at him. Was he revealing to much? Was he being obvious?

Taking a deep breath he thought about the main question.

"How?"