The First Law of Thermodynamics states:

"There is a state function E, called 'energy', whose differential equals the work exchanged with the surroundings during an adiabatic process."

In other words, energy cannot be created nor destroyed, only converted from one form to another.

TŌMA TILTED HIS HEAD back and stared at the ceiling, resigned from his studies.

He recalled Biribiri and her electrical abilities. He pictured the bridge where they met for the first time, the metallic smell in the air of cold steel. She tossed the coin in the air and flicked it past him at three times the speed of sound.

"Her electricity," he started to himself, "Where does that all come from?"

He scribbled some calculations in the margins of the textbook. A coin weighs about six grams. Multiply that by velocity – 1020 m/s – squared, becomes 1,040,400 m2/s2. Multiply that with the mass and divide by two to get kinetic energy – 3121.2 joules. That's more than the energy of a bullet from a hunting rifle. And don't forget that that's only the energy of the coin and not the electric field she used to propel it in the first place!

Tōma fingered the pages of his physics textbook and glanced outside. The last strings of sunlight hung in the sky like Christmas lights in February. Gray clouds rolled in from the horizon in anticipation of rain. He wondered if Biribiri could call a thunderstorm if she wanted to.

He needed help on his physics exam tomorrow. Only thermodynamics stood between him and a good grade on the test, but Tōma was lost in the pages. Concept after concept picked up, scanned, and then dropped, never absorbed. After an hour of reading, he still had no idea how to calculate the temperature of a cold reservoir in a Carnot engine.

He sighed and dialed the number and lifted the phone to his ear with his right hand.

"Biribiri, can we meet at the library? I need help with something."

"Tōma?" said Biribiri, "Isn't it going to rain soon?"

He switched the phone to his left hand. "No, I don't think so."

The sky was overcast by the time Tōma arrived at the library. He spotted Biribiri leaning against the door outside.

"Hey, Biribiri!" said Tōma as he waved.

She glanced up and swung her hair into the air, suspended. "How many times do I have to tell you? It's Misaka Mikoto." Mikoto shot him an annoyed look and crossed her arms. "So what did you make me come out here for this time?"

Tōma sheepishly produced his physics textbook and constructed a weak smile. "Thermodynamics," he said.

"Oh," she said in surprise, "Compared to the other things you're involved in, this request is abnormally … normal." She reciprocated his smile with her own. This was the first time he'd seen her wear a smile since last week.

They entered the library to find a quiet horde of students eating away at mathematics and Japanese history. The grand space lay before them adorned with Victorian furniture, Persian carpets, good manners. Old books lined the walls, and the shelves penetrated up from the first floor through the rest of the five story complex. A few students looked up to find Mikoto, one of the seven level 5 espers in Academy City, in the same presence as them. Whittling whispers filled the room to accompany the musk of academia. Mikoto ignored their stares and turned to Tōma.

"You're lucky, you know?" she said as they found an empty table, "I know a lot about thermodynamics."

"Yeah?" he said, "Then do you know about the first law of thermodynamics?"

"Of course I do! It's the law of the conservation of energy!" she said. Tōma was impressed. Mikoto wore a look of satisfaction.

"So tell me," he said, "Where exactly do you get your electrical energy from?"

"Huh?"

She never thought about this. Where did she get her energy from? She pulled her hand away from her hair and a sharp spark of electricity followed. The students around her looked up and sank back into their pages as if eye contact with Mikoto would result in electrocution.

"Well, that's obvious, isn't it?" she said, "My energy comes from my cells?"

"Yeah, right. And where do your cells get energy from?" he asked.

"From my surroundings, of course. They're constantly taking energy from everything I touch!" she replied.

"Really? So If I do this –" Tōma reached for Mikoto's hand with his right hand. "What are you –" she started.

His fingers wrapped around hers, the creases on their palms crossing as a woven fabric. Despite the billions of joules of energy that her hand could generate, it felt airy and delicate like paper. He only met her hand for a moment, but he didn't feel any energy drawn from him. She snapped her hand away to the giggling of the onlookers.

"Wha-what did you do that for!" she said. She was red and ready to zap him to oblivion.

"I was just testing to see if what you said was true," he replied.

"Of course it wouldn't work!" she said, trying to cage her voice from the other students, "You used your right hand!"

"Oh," he said. Tōma reached for her other hand with his left hand. He clinched it as before, feeling nothing but her touch. "Still nothing."

She stayed silent for a beat, shaking in embarrassment. The blood slammed against her skin; she felt as if she was sitting in a pot of boiling water.

"Mikoto?" he said.

"You…"

A cold pain shot up his arm and the left side of his body went numb. He jerked back instinctively and raised his right hand in front of him. He could detect the scent of electricity. It smelled like a warm photocopier.

"Ow!" he said as he massaged his arm.

Mikoto only offered him a meek glance and said, "Sorry". She waited for the students around her to resume studying to eliminate the risk of a rumor swelling beyond her control. Surely, she and Tōma would star in tomorrow's gossip if she let any more reactions escape her façade. Tōma began to feel the stares running through his being as well. He opened his physics textbook and flipped to the chapter on thermodynamics. "Why don't I ask you about work and heat?" he asked. Mikoto, still aflush, nodded.

It began to drizzle.

The students around them gradually returned to their studies as Tōma exchanged questions with the railgun sitting in front of him. The persistent rattle of wind against the tall windows provided the exclamation point to her answers. An hour passed. It was dark now, and Tōma realized that he had wasted away another sixty minutes dropping concepts without absorbing them. Tōma looked up from his textbook to Mikoto, who finished explaining something about how negative and positive work related to the expansion of gases.

"So do you understand how to solve the problems with work applied to a gas now?" she said.

Tōma frowned. "I think so," he said. Mikoto crossed her arms.

"Hmph. You still don't understand any of this, do you?" she said. Mikoto wielded her disappointment as skillfully as her railgun.

"I think I'm done for now. The library's too stuffy anyway. Can I walk you home?" he said. Mikoto recoiled.

"It's drizzling outside, and I don't have an umbrella," she said.

"That's fine, I brought one," Tōma offered.

Mikoto hesitated.

"Fine," she replied.

By the time they left the library, the drizzle had turned to rain. The couple walked down the local road out of the way of downtown Academy City. A tenable silence floated between them as Tōma reached over and nudged Mikoto into him and away from the rain. Her hands were cold, shivering. She must have been blushing. Tōma couldn't tell; he didn't want to know. She leaned into him, head on his shoulder. An earthy petrichor overcame the smell of ozone that clung to her. Tōma wondered if walking beside a human lightning rod in a potential thunderstorm was the wisest course of action.

A human lightning rod, Tōma repeated to himself.

What was Mikoto? A dynamo, a railgun, a force of nature. Level 4 espers had tactical military value; level 5 espers could take on an army by themselves. Misaka Mikoto could send out an electromagnetic pulse and obliterate every transistor and circuit in a 200 mile radius. If she wanted to, she could cast the entire world back by three centuries and vaporize any living thing who tried to stop her. Only two espers, Accelerator and Kakine Teitoku, were more powerful than her, and both of them were incapacitated. Tōma arrived at the disheartening conclusion that at the moment, Misaka Mikoto was the most powerful being on Earth. And this being was leaning on his shoulder, holding his arm in a warm embrace. What was Mikoto to him? Just a girl, he decided.

"I think I know where I get my energy from now," she said. Her voice was swimmy.

"Where?" he asked.

They walked beneath the streetlights, passing through cone after cone of dim light. Tōma caught the torpor in her eyes every time a streetlight lit up her face.

"I remember now," she said, "Espers draw their abilities from dark energy."

"Dark Energy?" he repeated. Mikoto nodded.

"It's invisible. The ability of an esper is to channel that dark energy into real energy. Some people do it more effectively than others," she said.

"And I suppose you do it very, very effectively?"

A car swerved close to the sidewalk and threw a wave of puddle water at Tōma. Mikoto jerked up her hand and produced a bolt of electricity and vaporized the water before it splashed onto them. The car continued into the rain, Tōma and Mikoto stood motionless on the sidewalk.

Mikoto stepped in front of Tōma, facing him. A flash of lightning illuminated the sky. She found both of his hands as Tōma eased his grip on the umbrella. The rain began to fall on their bodies.

"Very effectively," she whispered.

They connected eyes and then shut them as they leaned their lips in ever closer.

A crack of thunder resonated across Academy City. It didn't seem like the rain would stop anytime soon. What misfortune.