I wrote a dark, sweet tale.
Here is the first part of the story.

⚠️Note:In this world, only those who have reached the legal age of 18 can manifest magical powers. Alice is a 18-year-old high school senior, and Damian is her classmate of the same age.

"Hurry, Alice! I detect an incubus signal inside the school! It’s coming from the gymnasium!"

Roll, Alice's companion who resembled a white rabbit, shouted urgently. Alice was sprinting toward the gym at full speed. Students finishing their after-school club activities turned to look at her in surprise as she dashed past.

Now was not the time to worry about school rules like "no running in the hallways." If an incubus had appeared in a place as crowded as a school, there was a high probability that someone was already being victimized.

The Incubi had appeared in this world without warning. They were the sworn enemies of humanity, violating women and draining their vital energy. Even if they provided pleasure, their acts were nothing more than unforgivable sexual violence. Once a woman's essence was stolen, she would fall into a temporary state of lethargy. If preyed upon repeatedly, she would become unable to forget the taste of that ecstasy, eventually longing to be held by the incubus in a state of pathetic addiction.

It was the duty of Magical Girls to hunt these creatures down.

By forming a contract with an alien being in the form of a mascot, a human could become a Magical Girl. 
In this world, one had to be over 18 years old to become a Magical Girl. It was a role that required mental maturity; without a seasoned spirit, the volatile mana was impossible to control. It was only after Alice reached her eighteenth birthday that Roll finally approached her to offer the contract.
Fortunately, she possessed a natural talent for it and had never struggled against an incubus before. However, the aura of the creature this time was fundamentally different from anything she had ever faced.

Behind the gym, after confirming no one was watching, Alice gripped her red pocket watch and channeled her mana through it. Her body was enveloped in a brilliant light as her form shifted. A large red ribbon adorned her chest, complemented by a soft, frilled skirt. Her hair turned a vibrant gold, matching her striking blue eyes.

"Let’s go, Roll!"

Alice rushed toward the gymnasium entrance.

Inside the empty gym, a lone boy in a school uniform stood waiting.

"Hello, Alice."

"Damian!?"

Alice cried out in shock. Standing there was Damian Blackwood. He was her classmate and the boy she secretly had a crush on. He was handsome, brilliant, and possessed a charming personality that made him the idol of every girl in school.

"This is a lie, right? There’s no way you could be an incubus, Damian..."

As she spoke, Alice noticed the color of his eyes. They weren't his usual warm eyes; they were a deep, predatory gold—the unmistakable mark of a high-rank incubus.

"You find it hard to believe, don't you, Miss Kingsley? But it seems your little companion already knows the answer."

Roll spoke in a sharp, warning tone.

"Alice! Don't let your guard down! He is a High-Rank Incubus. He’s a far more malicious monster than any of the weaklings you've defeated before!"

Even as she heard Roll’s warning, Alice couldn't stop staring at Damian in disbelief. Damian kept his calm smile and lightly snapped his fingers. In an instant, Roll, who had been perched on Alice’s shoulder, slumped to the floor without a sound.

"Roll!"

Alice knelt down and shook her companion, but there was no response.

"I only put her to sleep. Don’t worry," Damian’s composed voice echoed through the gym.

"Miss Kingsley—or should I call you Magical Girl Alice? You came here to fight me, didn't you?"

His voice was gentle, and his gaze remained steady. Yet, noticing the predatory glint hidden deep within his eyes, a cold shiver ran down Alice’s spine.

Alice bit her lip and nodded.

"Classmate or not, it doesn’t matter. I will defeat you. By taking down a High-Rank Incubus, I can protect hundreds of girls."

A satisfied spark lit up Damian’s eyes. Alice raised her hand, summoning her magical staff, and channeled her mana through it.

"Shining Arrow!"

She fired a bolt of light at Damian. But in the blink of an eye, he vanished and reappeared to the side, dodging it effortlessly.

"…He's fast! In that case…!"

Alice instantly wove a new spell.

"Shining Shower!"

A relentless rain of light arrows descended. She manipulated their trajectories, cornering Damian against the wall. Then, she released all her mana at once.

"Shining Burst!"

It was Alice’s ultimate spell. A devastating explosion of light detonated right where Damian stood.

The moment she let down her guard, thinking she must have won, her staff was violently knocked from her hand.

"…Ah!"

A surge of overwhelming magical pressure made her skin crawl. Before she could react, an arm wrapped around her waist, and her hand was pinned.

"…Caught you."

It was Damian. The low whisper breathed into her ear made her entire body jump in a visceral reaction.